I was wondering about this very thing, my smaller sites, some super-thin, haven't been touched by Panda 1.0 or 2.0...including my old, tired, neglected thin affiliate sites. Some have even seen a bit of an uptick.
My main site sailed through 1.0 but has been dinged by 2.0 (looks like a 25% hit).
This theory could also explain some of the results I'm seeing in my niche. It's settling into mostly big brands that have muscled me out and bumped me down a few slots, but there are occasional results with weird stuff too (blogs with just the title showing above the fold and up to 10 ads/page). I thought maybe it was the social media aspect but maybe it's just that they haven't been touched and are floating to the top because there's less competition for them.
Wondering if small sites are exempt or if there's a killer tsunami heading their way...but then who would fill the serps? Just big brands?
Question of the day: time to polish up tired old sites? Build out new domains?...or wait things out.