There are many happy users of the 17-55mm f/2.8 IS USM lens. It can produce great photos in the hands of the right person - as can a lot of other lenses...
The constant f2.8 is great for low light work, and to get a decent amount of subject isolation / background blur at the tele end.
I don't believe an update for the 17-55mm will be coming anytime soon though. One of the major reasons that I have for this, is that Canon released the EF-S 15-85mm f/3.5-5.6 IS USM a few years ago, ie a few years after the 17-55.
While the 15-85mm isn't a constant f2.8 lens, it does improve on a few other aspects of the 17-55mm:
- better flare control
- 2mm more on the wide end
- 30mm more on the tele end
- better IS (4 stops)
Some people argue the 15-85mm build quality is slightly better than the 17-55mm... but I'd say it's quite close.
Both lenses (17-55mm and 15-85mm) are very sharp, have good contrast, make use of Canon's true USM focus and benefit from IS (3 & 4 stops respectively). So they are great 'kit lenses', which each meeting differing photographer's needs. (The 15-85mm meets my needs much better in a 'kit lens' - eg when I want a fast lens, it should be at least f/1.
So while there might be a 17-55mm II sometime in the future, I expect that is probably around 4 or 5 years away at least..... In the meantime I think Canon will be producing lenses to complement it (eg more dedicated / primes lenses).
I also believe that it's very hard to compare an EF-S lens with an 'equivalent' EF (ie FF compatible) lens, due to the differing nature of focal length, DOF, etc - although f2.8 (on APS-C) will always let in more light than f4 (on FF) even if the background / blur isn't as affected as much. Then there is the whole argument about "difference in build quality between an L, the new prosumer lenses, older 'gold ring' lenses, etc, etc,". I won't even go there...
Best wishes.... and happy photographing....