I've recently made that very same switch. I'd been a happy Be customer for 2.5 years, and will still recommend them to people who have them available but no FTTC (or who don't need (or don't want to pay the extra for) FTTC).
I was connected on Friday and I've been most impressed over the 6.75 days so far. I've had two problems: a line issue that is BT not AAISP so I'd have had that with any ISP, and a reverse DNS issue that was fixed quickly (and may not be something you'll even care about). Response from AAISP in both cases was very good, even at the weekend.
Line speed is excellent. I'm getting the full 10Mbit (well, as near to as makes no odds: 9995K) upstream sync which works out at an observed rate of 8.something on speed tests (1070KByte/sec when I set an throttled torrent going to see how far I could push it), though obviously you might not get that much depending on your line (check with http://dslchecker.bt.com/adsl/adslchecker.welcome
- it guessed I would get 32down and 7.8up so either that was quoting expected observed speed or the figures were an underestimate as I get 35d+10u (it may, or course, overestimate in some cases too)).
The downstream sync I'm getting is ~35M. Observed speeds have been more variable than upstream but that could be the other end of the communication not being able to keep up with my shiny new link or congestion on BT's part of the arrangement. I've not tested this much, as upstream was the important thing for me, but when I have it has always come out better than I was getting on ADSL (12Mbit), usually significantly better.
Current ISP: Andrews & Arnold (AAISP, aa.net.uk) via FTTC at ~36Mbit down & ~10Mbit up, joined July 2011.
Previous setup: Be Pro with UploadPlus (ADSL2+, AnnexM), 12ish Mbit down, 1.6 up, happy customer for ~2.5 years.