You can get up to 8MB DSL Broadband (subject to being able to receive it) and a 40GB monthly download limit, which they say is sujbect to a fair usage policy.. So if your hammering your connection every month they'll probably either charge you for more bandwidth or just cut you off at a certain limit.
I cant complain over the free UK calls and calls to TalkTalk Mobiles, however I'm sure there is some catch built into the smallprint. Of course check out their Tarrifs for calls that are chargeable, theres a difference of up to 17p on some calls depending on the time of day you use it!