Pros: Big, fwd sound; SPEED/DYNAMICS; soundstage; durability/ day-to-day reliability
Cons: Poor isolation; poor canal fit (may slip out); muddy bass
Own several "high-end" tradl. 'phones (Senn 650, 600, 580, bd 880 Pro; AKG701, Grado 325i; etc.) and IEMs (SM3v2, SE530).
>> The IE8s are my go-to cans for any use. <<
Some one else noted (and I agree) "tunable bass port is almost useless". Even at min., there is almost too much bass (which is non-tight and a bit muddy). This feature is a gimmick. Sennheiser should invest our $$ into other aspects of IEM design (isolation, better tips, etc). Better yet, get rid of this gimmick, and all that worthless packaging/boxing, and reduce the sale price.
At 2+ hrs/day of use, they took over three mos. to PROPERLY burn in!
Isolation is very poor. None of the stock tips help here. The Comply doped-foam tips are okay, but they don't last long. Comply's are also very hard to fit on to the nozzle. I snapped off both (L/R) nozzles (which, thank goodness has a soda-bottle-cap-like break-seal thread) trying to twist one on/off. But now, both nozzles are no longer affixed :(
The Comply is also more PITA to use: roll/insert/wait for it to expand. By sheer luck, my Teclast T51 DAP came with a pair of free IEMs (R8) with extra set of tips. They are double-flanged and tapered -- somewhat like Etymotic -- silicone types and they fit the IE8 nozzle very well. By far, the best overall IE8 tip I've used. Dunno how to buy these separately, tho'. (Note, the Teclast R8 tips I'm talking about are not the ones in the R8 photo --- they are additional tips that come with the R8 package).
All that said, this unit is going strong after 2.5 years of 2-3 hrs daily use. The transducers seem indestructible (typical Sennheiser!!) -- still do not distort despite my DAP/amp's massive on/off thumps, and sometimes high volume demands ;)
Comparing: My Shure E2C and SE530 cables "rotted" away after 9 mos.! The Shures and Westones simply do not compare WRT sonics ... IMO. Maybe, I don't like BA sound. I'll try the SM3 v2 shortly.
They are my fave head-/ear-phone ... period (uh... full stop for the UK!)
Noticed few comments on PRAT (pace, rhythm, acceleration, timing), tempo/speed (fast, slow, so-so), dynamics (macro-, micro-). The 8's are the best I've heard on all these qualities and attributes. No I haven't heard them all (e.g., suspect FX700 may be better for speed). I just compared them to new (as of 2011-06-01) SM3v2s. Still way prefer IE8s.
It's very important to break them in for at least 100hrs (use XLO CD's burn in track).