According to the change log, the biggest changes seem to be with the Blackface Deluxe and Blackface Double models, with improvements in other amp models with high gain pickups. I'm using a JTV so I'm not hearing a big difference with the other amp models, but I do hear the improvement with the Fenders.

They have said that this is a bug fix release, but new features will be available soon. Check the change log to see the fixes.

I think on the whole every amp model sounds better, but there's a real difference to the Deluxe. It was good before but it's simply fabtastic now. For my ears it just seems to have better compression now, it's just so much tighter, it's brilliant, I haven't stopped playing with that 1 amp model since the update I love it Now if I could only have my Citrus when the new goodies come out I'll be 1 very happy customer

Nothing on the whole sounds better with the update IMHO. However, the controls definitely react differently in the lower gain registers. In some amp's this results in needing to adjust the gain knob up to get a response similiar to before the update and in other cases it provides some additional clean headroom down at the 9 o'clock and under range which wasn't there before. This wasn't any type of magic bullet which changed the overall sound of the processor.  I imagine those who didn't like it before probably still don't like it....