Contents of .bookmark_thumb1 I've got one of these folders on my HTC Desire 2.3 and I'm assuming that it's standard across all devices. It looks to contain screenshots of pages that I have visited using the built in browser and I'm guessing that it's to dispaly them in the bookmarks/frequently visited list or when I'm changing windows.

My question is is it safe to delete the contents of this folder? It doesn't occupy much space but there are sites in the list that I know I won't be visiting again and it seems pointless having them around.
Yes you can safely delete the folder. For details and a permanent solution (to stop regeneration of this folder) check this