Why would you want to trash the case of your filenames by always converting to lower case? Seems that you're losing something there if they already have meaningful case. And (assuming you're using an OS where case matters) you could clobber an existing file by doing this if the filenames differed only in the character case.

(I guess if you're using Windoze, though, you haven't yet gotten used to using upper and lower case in your filenames)