Pros: really impresive sound quality and good soundstage, value master due to koss lifetime warranty, no need to amp them, really portable
Cons: hair ripping, can't be worn around neck, not the most comfortable to wear, cable tends to break, hair gets under the membrane, leaks music
Porta Pros simply made the biggest difference for me when listening to music as I have switched from some low-end sony in-ear to them and suddenly when playing the same song music became more rich and colourful and instruments more noticeable soundstage improved and on top of that really nice bass for me as I listen to classical rock or big beat and those bass makes it more pleasant for me. One thing I hate is how in past few years quite a lot more people started to use them and they can't appreciate the music as they are just kids listening to recycled audiosmog king of commercial waste.
If you are concerned about bass being too strong there are some mods that are supposed to deal with it and either bring out the mids and highs or weaken the lows, p.e. Kramer's mod, using HD414 pads.
Some people says they are not portable enough or that the when folded in bag it not practical, on the other hand form my experience I found that while carrying in the small bag is pretty good when packing or travelling and space is an issue, but the most notable advantage is that they are so much more durable when in the bag, because of fragile cable and if you wear the around your neck other than discomfort cable breaks a lot quicker.
As mentioned comfort is bit of an issue. Forget about them hanging around your neck but if you have either longer or curly hair they will get caught and ripped by them and like once a week and it can be really painful. Also if you are using them for more then 2 hours or so it gets fatiguing and you feel them pressing your skull. It gets a little better when they are worn in but if you plan on using them for longer periods of time I advise you to switch to a light comfort zone and then it's absolutely minty (although they don't hold on your head as firm).
But other than comfort and weak cable Portas are wonderful, they have sweet old school design that really grow on me, also are very lightweight and music experience is sensational, on top of that the are delivered with koss lifetime warranty so they are embarrassingly inexpensive. I have paid for mine and 6 new ones due to warranty about 90 bucks, so there goes the value.
For the final verdict: go and pick yours today or if you are concerned with comfort pick the Koss KSC75 and enjoy the music.