c-bert,
As dublinpilot says, make sure you get your licence signed by an EXAMINER beforethe rating expires. Even if you've done everything, and you're a day late, they can't do it.
As I understand it, the proficiency check/skill test is a scaled down version of the PPL skill test, but it doesn't include nav or anything like that, and is just what it says - a check of your proficiency. At least, that's what the chap who gave the talk said. He said that people who hadn't got the 12 hours could just get up to speed, flying an hour or two with an instructor if necessary, then do the proficiency check with an examiner, rather than spending lots of dosh trying to get the 12 hours. If you do this check in the last three months you won't lose any time on your rating, ie it will run for another two years from when it would expire.