I have about one million different Microsoft Visual C++ Runtimes installed... 2005, 2008, 2010. Can I remove some of them, or will I have issues?
You should be able to remove the versions you no longer need as each is a separate installation and they run side-by-side with no issues (that I know of).
If you want to be 100% sure you could uninstall them all and then reinstall only the ones you want to use, but that shouldn't be necessary.
These runtimes are installed by programs that need them, and generally left after you uninstall them. This is done for two reasons: 1, they're shared between programs so it's hard to figure out if there is another program relying on them. 2. Since they're shared, and because they only use CPU time and RAM when actually used, there's little profit in removing them when unused.
You would have to check if all your programs still run after removing one of them. If not, you would have to reinstall the runtime, so make sure that you only remove the ones for which you have a download link.