My money is on Tiscali as well.
I play a well known MMORPG and several people I know have had problems connecting to that and other sites/services due to Tiscali. They are not as bad as AoL (Almost OnLine) but are working their way down there.
Personally i have cable internet (Telewest) and have pretty much an un-interrupted service for the last 2 years with them apart from 2 times, one of which lasted 15 mins and for the other it went off at 1am and was on when I got up in the morning. It has to be said though that while my experience with them has been good it does seem to be very dependant on your area as I know people in other areas to have problems and oputtages on a slightly more regular basis.
In short…
Douse you Tiscali cd’s in petrol and throw them into the incinerator and get another ISP…