How do I check my Mac's RAM? I know there is MemTest86+ for PCs, but what can I use to see if my RAM is actually good in an Apple product? Whether it's a MacBook, MacBook Pro, iMac or Mac Pro? What symptoms would show that RAM is bad?
I've had bad RAM that still allowed the machine to boot - a stick of memory in my Mac Pro apparently failed gracefully overnight. 

The first step would be to check system profiler to see if the memory is being recognized. If indeed it is, there's a version of MemTest for OS X: http://osxdaily.com/2011/05/03/memtest-mac-ram-test/