OK, it's now over a month since I switched to Be as my ISP, maybe it's time for a status report.
Basically, there's nothing to report. It's working, and working very well. I don't think I've had any instances of the connection dropping to low speed or going dead altogether, which was a fairly common thing with NTLworld once Virgin took over, there's no sign of any throttling back, and downloads etc. are very fast indeed.
I'm delighted, and given that there's no sign of BT rolling out fibre in this area any time soon I don't expect I can get a faster service. Since I suspect that Be's fibre service will use the BT lines once it gets off the ground I will probably stick with them anyway.
The bottom line, I thoroughly recommend them.