LPT: If you're invited to a wedding, put it in your calendar as an all-day event that recurs annually. Then, in later years you can surprise the couple (and gain kudos) by wishing them a happy anniversary.

You can do this seperately in your calendar of course (or not bother at all, if you don't know the couple well enough), but I find I'm much more likely to remember this way. People seem to really appreciate it, as you don't tend to get poked by Facebook etc. for people's anniversaries.