Also, the last time my BE broadband died for about 6 hours during the day (which has happened twice in 6 years), they refunded me an entire month's bill. Do Sky, Virgin etc. do that? My line has remained fully-working apart from those two incidents at constant 20mbit connection speed. I'd say that's pretty good. Their DNS problems are bad but I just use Google's DNS and have had 0 problems.
No idea, my Sky connection has never dropped out in the year I have been with them, its also never dropped below 16mbit (which is the maximum speed my line can achieve given distance from the exchange). I am also on a 12 month contract where each month is the same price.