Commonly Solved Problems
Google just introduced Code Search, which lets you search "public source code", which I imagine is every OSS project they could lay eyes on. My first search (because I was just looking at the new version of commons-lang), was for "file:StringUtils.java".
There were about 400 hits.
There were even lots of different StringUtils classes in different apache products. Though, it is clear these numbers are slightly inflated, as different versions of the same file come up.
My, but we love to solve that StringUtils problem :)