I have Sky Broadband. You do need a BT line, but use their cheapest option, because some telephone calls - evening and weekends are cheaper or free and are included in the Broadband package. I am happy with the service from Sky, and have had no problems with connection or speed..
it's just Sky broadband, not Sky satellite broadband.
Sky's broadband service is exactly the same as any other providers broadband and is supplied over a phone line, it has nothing at all to do with satellites other than your paying somebody that also runs a satellite TV service.