For the most part Hulu is pretty useless for UK residents since it's geo-locked to the US. We can't watch re-runs of NBC, Fox and Comedy Central shows.
But there does seem to be an exception - Dr Horrible is available on Hulu and doesn't seem to be restricted to the US which is just as well because it's not available through the UK iTunes store so this is about the only legal way to see it. It's thoroughly good fun coming from Joss (Buffy, Firefly) Whedon.
[UPDATE] Oh well - it was good while it lasted. It's no longer available in the UK.