There are not as many "optimizers" for OS X for various reasons: first, there's no registry, second, being a smaller market, there's much less crappy software, otherwise it could not survive. But there are uninstallers, that's for sure, config files are often left behind when uninstalling.
Going back to your question, both Total Uninstall and Regshot are able to do that, although with Regshot you have to do the removal by hand. And yes, after uninstalling a trial version and installing it again, you get more time to test the program, I tested this personally. Be aware that some software write data to certain system files for their trial systems, and the uninstallers can't remove this data, but they can tell you which files were modified, so you can remove the data later with your favourite text editor.
The best option is to use something like Sandboxie, as kreatorr notes above, or any VM, like VirtualBox or Virtual PC.
BTW, the task of uninstalling an application correctly does not belong to Windows, but to the guy writing the uninstaller of the application you're using. Most software do not leave junk behind, as long as they don't write too much data to the registry or scatter files around the file system. The bigger an app, the greater the possibility of bad uninstallers.
