I know of many Deviants here who've either left or stopped uploading artwork because of idiots who stole their work online. It's a sad side effect of the accessibility of the internet - incredibly wide audience, but easy to copy.
IMO the best way to deal with this is watermark/sign your website on there, and use it for publicity. But of course this doesn't work in all cases.
I just ran across a great tool to see if your work has been stolen, a reverse image lookup tool called TinEye: tineye.com/
Also, the firefox add-on, which makes it real easy to search: addons.mozilla.org/en-US/firef…
Easy way to find your work, how it's been used, and pursue action if warranted.