little - your LP is meant to be about the same length each cycle (to within a few days), so it probably isn't shortening even if your cycles are. I am a bit of a medical anomoly on this point, though, as my LP is variable, so you never know! As far as I know, a short cycle doesn't mean your LP is also short. If you have variable cycles, it tends to be the follicular stage (between the end of your period and ovulation that varies in length. You could try charting (if you don't already) to see how long your LP is? o you use OPKs or the Shag Dictator so you have some idea of when you ovulate?
Still no AF, will be so blimmin' depressed if I get it today, though. It wouldn't so much be the not being pregnant (although that would be obviously also be teh suck) as the fact that despite shovelling down vitamin B6 like its going out of fashion, all-but giving up booze and subjecting myself to acupuncture, my luteal phase would have gone back down to 8 days when I'd managed to eke it out to 10 days last cycle.