Create a database with few thousand collections, try and drop the database. For a database of only a few hundred megabytes, took over a half hour to delete. "show dbs" was hung during that time as well. If I just create a database with one collection and one document, I can delete things just fine.

I'm currently graphing all metrics from serverStatus so let me know if theres any values you think are relevant to help debugging the issue. I'll add more information to this issue as I find it since I'm still running tests but wanted to get the discussions going.