I've been using the E500PTH for about a year already, among the 1st to pre-order it. Till now it is the only earphone I listen to. The others I had like ER4, UM2 are sleeping the in drawer.
If your source is just an iPod with low bit rate mp3s, the E500 might not be a great idea. It shines with high quality source and an amp but it is still enjoyable with just an iPod, just that you will not 'fully' experience the E500 sound.
In the Shure line up, I think only the E4, E5 and E500 and its SE equal counterparts are worth considering.
The difference between the E and SE models are the modular cable design in SE series. E series are standard single long 1.5m cable. SE series features short 50cm main cables with 9inch and 3 feet extensions. So u can use it with remote controls or as standard.
Also, different ear tips have different results/sounds. The upper range Shures comes with all sorts of tips avaliable. U have to try them out to see which is best for you.
To me, the PTH device is quite useless. Mine is still in the box. Because of such earphone's isolation ability, you can't hear what is going on outside. Ambient noise is isolated. So when someone tries to talk to you, you have to remove the earphones to hear them.
This PTH allows you to press a button and ambient sound/noise is transmitted to the earphones via a mic. So you need not remove your earphones. It is design specifically in mind for foam tip users as foam tips wears out really fast if you keep putting/removing them. It will be costly to constantly replace them.
As I'm a silicon tip user, I just remove the earphones and keep that PTH in the box.
If you want to buy mine, I can sell you.