I disagree with that Chewy... a lot of C4 programmes are sensationalist documentaries (like the ones on at the moment about the world's most intelligent child / largest breasts... not to mention the Dispatches and Food Season ones too). Big Brother is tired. Hollyoaks is just terrible.
There is some good stuff though, such as Shameless and Peep Show
As for daytime TV however, C4 has it spot on. Countdown, DonD, Come Dine With Me, Paul O'Grady, Wogan's Perfect Recall, The Simpsons are all good TV.
But I think BBC has a lot more variety, and is generally more popular. Although I don't like shows such as Eastenders, there's good drama, children's TV and informative programming too.
To go off the top of my head: Heroes, The Apprentice, Spooks, Hustle, Survivors, The One Show, Masterchef, QI, Never Mind the Buzzcocks, Have I Got News For You, Question Time, Newsnight, University Challenge. Then BBC Three and BBC Four have good programmes too.
I think, though, that with a bit of creative and monetary injection, C4 could be on par.