After much debate, I picked up a TB this last weekend. The phone is a beast, and I love it for the most part (rapid battery drain aside), but the hp jack does have a soft hiss when I'm listening with my IE8's. It is rarely noticeable when music is playing, but it is definitely there when the music stops.
From what I can tell, the hiss kicks in when playback is enabled but its level has no relation to volume. It is most blatant for a second or two after pausing playback. Then the HP circuit apparently cuts out and the hiss vanishes. Otherwise, the playback quality is decent enough for a phone I suppose...but the hiss may be a deal breaker for some.
Personally, I'm finding the insane data speed more than makes up for it though. LTE is simply surreal after living with AT&T's basically worthless 3g network (in Los Angeles) for the last 2 years.