Just installed 4.0b3 and been playing with it about 15mins. So far not so good. Not quite at the point of dumping it (again) but I can't see it being as usable as the latest Opera or MicroB.

Biggest issue so far is the still laggy UI. Tabs are ok, but IMO still not quite as slick as Opera's.

If I was still using FF on the laptop, syncing is/would be a big plus, however in my case FF is the back-up to SRWare's Iron (Chromium) browser.

Start-up speed was definitely faster than previous builds from mid-2010 (iirc) and compared to MicroB performance seemed similar when on WiFi and 3G.

But, the UI is still the main stumbling block for me.

It's a pity, I really would like to see Fennec on par with MicroB and Opera. At the moment, I'll still have to give it a couple of more versions untill I dump the other two.