If you don't mind me asking, does sky also provide unlimited internet like Virgin and cheaper as well? We have a few days left before we can cancel our year's contract and since virgin have been pissing me off with almost everything lately, I'm dying to switch to something else especially if it's cheaper. We're paying about £22/month for just the internet.
Problem with Sky is that I don't think you can get the broadband without the landline or at least paying line rental. It looks like it starts out cheaper, but after 6 months, it would be more expensive than just Virgin broadband, and possibly slower if you live in a fibre optics area. However, if you have a landline and were willing to switch it to Sky, it's really a cheap bundle. If you opt for the £5 international unlimited (free calls to a list of countries, including US. You just need to hang up before an hour is up and ring back), add the line rental, and the discount, you are looking at around £27 for unlimited broadband plus most if not all calls.
This is what I found for you:
http://www.sky.com/shop/broadband-talk/broadband-options/broadband-only/I don't think it works out to be cheaper for everyone. It's definitely dependent on individual usage, but for us, we're paying £25-40 a month less, getting more channels, and actually have had fewer outages on the broadband than with Virgin. The satellite can be a bit more temperamental, of course, but even the telly has been up more than Virgin.
We actually ended up with fast broadband (or at least comparable to what we had with Virgin) with Sky because we were never eligible for the fast Virgin cable internet.