2-year sleep regression?

Can we talk about a 2-year sleep regression? I have 6 (six!) emails within the last three weeks from people with 2-year-old who suddenly aren't sleeping through the night or as long as they used to. And most of them are still going to sleep OK, just not staying asleep.

I'm wondering if we can pinpoint when exactly a sleep regression at this age happens. I'd add my two data points, except I honestly can't remember much about either of my kids' sleep habits at that age. Perhaps after the monster 18-month sleep regression my brain just failed to register anything else? I do remember the 3.5-year PITA-ness that also led to all kinds of attempts to negotiate going to sleep. But everything between about 21 months and 3 years, sleepwise, seems to have slipped out of my head.

So, please post when your kids stopped sleeping (if they did) around the age of 2 (so far I'm getting several votes for 27 months). And if they stopped going to sleep initially, or if they started waking at night (relative to how often they were waking before), or both. And if they were in a crib, big kid bed, or cosleeping.