As a home user (on Datastream not LLU) I find the service o.k for the money, at the moment I get a 2Mbit service for 29.99 a month. There has been some trouble recently with contention on their main piped apparently but this has bee rectified and most customers are speeding along again. Their LLU exchanges are getting good reports on ADSL guide and for the price it looks like a great product.
However for a business user I'd recommend caution. Their DNS servers are up and down like a tarts knickers and their residential faults line is dire. I rand the other day about our line being down (first time in about 8 months) and the first line tec didn't even know how to ping my router! He just filled out a form and said someone would contact me the next day. Obviously I wasn't happy and insisted on speaking with a manager, but they said exactly the same.
While waiting for the callback the line came back to life (about 1hour after reporting it) but I never received the call back. I rang back a few days later and they were good about it, apologised and gave me two months free BB.
On the whole for the money I think they are great for res customers, but if you rely on your connection to run your business I'd be very cautious before taking on one of their products.
HTH