Since switching to Tiscali a while back, I've noticed my internet connection suddenly 'dropping out' a lot of the time. Maybe once a day, I suddenly lose connectivity. Maybe for no more than a minute or two, but it was getting very annoying. Might be my fault, might be theirs, you never quite know.
So I found a piece of free software called Link Monitor, which sends a 'ping' signal to a website of your choice every few seconds, and alerts you when/if the signal doesn't get through. All the details are logged in a simple text file. The results? - it isn't anywhere near as bad a problem as it seems, but it is happening relatively frequently: actually, three times in the last 15 or 20 minutes. 
Certainly I never noticed such problems with NTL.