I have updated this review in a few spots from its original posting, for accuracy and nitpicking
lets get the formalities out of the way first
I hate IEM's, let me count the ways:
I hate plugs shoved in my ears, i hate that every little movement or chewing, or wind blowing causes seismic activity in my head when i wear IEM's. I hate how they fit, i hate how they feel, i hate foam in my ears and waiting for it to expand, and i hate how they fall out or if you even wiggle them a touch you lose all the sound quality, i hate how they sound, i hate having to pull them out ever time i want to have a conversation, and finally, i hate not being able to hear anything around me at all because i hate being hit by cars.
I owned the s4i's and returned them. they sounded great, they even felt pretty good, and i almost kept them, but at the time they didnt work for my context of needing to hear someone at all times that was walking with me.
most headphones i put on/in, especially IEM's within about 2 seconds i either say yuk and toss them aside, or say hmmm... these sound pretty good, and begin critical listening to decide if really like them. These definitely passed the hmm test, and the critical listening test
I needed some headphones for flying, and after exhaustively searching i decided i could tolerate IEM's if only just for flying, because i dont want to take up the extra room with a full set of noise canceling cans, not to mention most of them don't pass the hmm test...
that said... I love these IEM's let me count the ways:
i usually eq my headphones at home but of course with iem plugged into an ipod thats not an option (barring the ipod eq which i usually dont like), and thankfully these little guys delivered. NO EQ necessary
lets get specific
FIT/comfort: klipsch eartips are the best, they are like soft little teddy bear being crammed farther down your ear canal than any q-tip should ever go. but really, coming form someone who HATES HATES HATES how iem's feel, fit, etc... i was astounded.
usually when i wear iems i fit them to the outside of my ear.. in other words theres the main hole, you can stick your finger in, and than there is the deep q-tip only region that i would never dream of sticking anything in without extreme caution, lets call them the canal, and deep canal for our purposes
so usually i fit to the canal, i use either medium or large tips and get a good seal.
this time though for some reason, i took a look at those weeeeeee little guys and asked myself, how on earth would these fit anyone? so i put them on, and of course they made no contact, then i said, ok, im going for it, and i pulled my ear open and shoved them WAAAAY the hell in my deep canal. pressed play, braced for impact, and WOOOOW did it sound better, and especially odd, was it actually felt better, fit better, stayed in place better, and eliminated almost all that annoying cable noise, vibration noise, etc...
then i tried the double flanged tips: Heaven on ears.. ive never felt something so deep in my ear that felt so natural and comfortable. the sound was outrageously good.
with the double flange seal, and the tips so far in, combined with the cable tightened around the back of my head, i think i could win a wrestling match without these things falling out... very impressive
ive even tried keeping them in for long periods.. i cant believe im saying this, but i hardly notice they are there. they feel great! its a freakin miracle!
i also find these tips very easy to get in, position correctly, and get out.. simple, no nonsense, no fiddling, stick them in, press play, done... some iems you spend longer getting them "just right" than you do listening, then a knat lands on one of them and you have to start over. definitely not the case here.
with the tips in the canal, the sound was almost perfectly balanced. highs were a little overblown, symbols were a bit too much for me, and bass was balanced, but a bit lacking for my taste, especially in the kick drum and bass guitar regions
with the tips in the deep canal, particularly double flanged, the sound deepened substantially, the bass came alive, the kick drums and the bass guitar felt much more real and deep. and the rest of the sound rolled off just right. the highs were now perfect.
the overall sound stage was fantastic, the instrument separation and precision were great.
i havent actually tried these in a plane, but the sound isolation in every other context has been awesome. I cant hear anything around me unless its really loud and acute. GREAT
Construction: weeeeeeeell, i certainly do feel the need to be careful. for such a smaaaaaaall footprint i would be careful with any iem's though. also the little rubber parts that protect the cable at the end of the buds, and the end of the plug are bit weak. but overall, they feel solid, and i dont anticipate any outage or breakage as long as i dont try to win said wrestling match with them in any time soon
looks: when fitted with small, or double flanged tips, they simply dissapear. I like that.
OVERALL: i cant say ive tried lots of high end IEM's, but i have tried a few, and plenty of lower end ones too. These are by far my favorite. not only the only ones ive ever been able to tolerate, but really really nice. they feel great, they sound great, the fit and stay in place, they are TINY.
I would give these IEM's a 9 (updated from 9.5) out of 10 b/c they are a bit fragile, and overall, they still have that IEM sound.. I would highly recommend these to anyone looking for some IEM's, for travel, for activity, even heavy activity, for extreme sound isolation, for long haul listening, they deliver in spades.
regarding the claims that they are a bit bass heavy, yeah you might say that, or you might say that thats how bass should sound.. its so hard with bass b/c everyone has unique preferences, but if you use shallower tips, the bass tones down, however they dont stay in quite as well, and the vibration cable noise increases a bit. It should also be noted that klipsch, on their own site gives descriptions of the difference in sound between the x5 and x10, and they claim the x10 have more bass...
UPDATE: one thing i would add, is that yeah i guess the bass might be a bit heavy for some, and also, when i switch back and forth from my full size cans (d2000's) i realize what im missing in the IEM's.. they just dont have that broad, even can feel.
if i had 2 recommendations with these i would say - get the x10i so you have the mic and remote, and get them used so you dont have to pay a gazillion dollars for them. They cost about $350 new and you can get them on head-fi for, well... a lot less anyway ;-)