Often when you open an XML config file in a DTD/Schema aware editor, and you're connected to the internet, the editor will reach out over the net to fetch the DTD/XSD, which gives webmasters some interesting usage stats.
I've commented before on how you can use this technique to look at the big growth in DWR usage, but I noticed that you could also use it to suss out some JVM usage stats because when Eclipse etc come read the DTD they use the Java version number as their User Agent.
Anyway, the numbers:
Caveat - there are about a million reasons why this is un-scientific. It may be interesting to some though.
Aside: I wonder if Java should adopt the 'standard' formatting for the User Agent string that is employed by all major browsers?