The SERPs for the UK have been changing a lot. I think it's live, and if not 100%, very close to it. Google rolled it out on all of their major networks from the beginning of January.
NO IT'S NOT ACTIVE. If it were active i think Matt Cutts might have something to say about it on his blog. Until Google or Cutts officially anounnce the implementation of Caffeine then it is NOT live.
I dont think anyone can actually confirm caffeine is live with any authority apart from Cutts or G, this guy seems to be on the data centres pretty often but yet again he doesnt have any authority so its all just guesswork, http://jimchristian.me/ heres his blog, take a look for yourselves.