Still getting used to it folks - very happy so far though.
Overall, in comparison with the XT I'd say I get more top-end bite (which I was always searching for in mixes) without so much added "fizz".
Having said that, I lean more towards "older" blues/rock tones. I was specifically interested in the fender and vox models - I've never got to full "happiness" with the XT versions. Within 10 minutes in the shop I knew the Tonelab was going to deliver on that. Also, the early 80s M/V "marshall" model works a lot better for me on gain of around 5 or below - I can actually model how I used to use my own valve amp live with it!! Bliss! (That's an early 80s Laney Protube 50W M/V, a year or two before the AORs came out - basically a Marshall M/V clone)
Jack, I've heard that about hi-gain on the Tonelab as well. I haven't tested too much down that road yet. What I have found is that there is an "authentic" valve-amp hiss that I suspect will become more apparent with higher gain. There is a noise reduction setting, but I tend not to use those in a modeller, I limit it in the DAW afterwards, I seem to have more control that way (and I hate the sound of "noise" decaying with the note while I'm playing!)
In addition, the Tonelab feels much more like playing through a valve amp. I've never used a real valve amp for high gain - and I suspect that if I want high gain stuff (in my environment, that is, a home studio/living-room) that I will prefer what seems a more processed sound from the XT. But for good ole "blues/rock" tones, the Tonelab is a stunner.
Andy, yes, I believe you can turn off the Amp sim but it does remove some other functionality (can't remember what, I don't do it so my eyes glazed over when I read about it! - go to the VOX site, you can download the manual, it tells you in there. I downloaded and read it before I went to the shop so that I had half a chance when testing it!)
I'm not actually a big effects user. On the XT I tended to use the Sine Chorus, the EQ + Boost, and the Wahs. On the Tonelab, I haven't manged to learn a chorus I'm happy with yet, but I think I will. I was a little distressed to learn that the Wah counts as a "Pedal" effect (read "Stomp" for the XT) - but I'm not missing the ability to have the boost and the Wah together. I will say this for the various "Pedal" effects - OD pedals etc - they seem a lot more usable to me than the XT models. And the Wah itself - I was about to miss 8/9 different models - but no worries! You can configure it for one of two VOX models (changes the "notches" in the sweep), AND you can configure the tone of both the open and closed sounds - this is VERY useful.
Overall though, if you like the XTs effects - I think you might feel a little restricted with what's on offer in the Tonelab. It might be that quality outwieghs quantity though?! I'm not in a position to say really.
It does have an effects send and return - which is something I think Line6 have added to the X3 - but, again, I don't need it.
The ONLY quibble I have at the moment is no USB connection. I've downloaded the Sound Editor - nice and intuitive - but it does mean I have to get the MIDI/USB box, and find the cables, etc, etc, when I want to connect to the PC. But this is MINOR. I'm gessing that if they'd added USB, they'd have to be looking at including digital/soundcard type operation, and that would have pushed the price up.
Hope that helps guys!