I like to script things like this when I can, for many reasons. First and foremost, I prefer to write programs that do repetitive work for me instead of doing the repetitive work myself. Second, writing little helper scripts like this allows me to share them with my team, boosting their productivity as well. Lastly, as an exercise for me to learn and practice the obscure art of Windows batch scripts. Here is the command as it would be run from a prompt in the root directory where you want to delete .svn directories:
for /r %R in (.svn) do ...