Tiscali do slow you down if you download a certain amount in a month (8gig I think). However, if your on Tiscali I wouldnt worry about ever hitting that limit. If you want good value for money, no cap and a fast connection (I actually get 18mb/s down and 1mb/s up) take a look at Be*

In the past 7-8 months I have only had 4 hours of downtime one evening and I think that was due to upgrades going on at the exchange.