A microvolt is all that's needed to fry a stick of memory/videocard or most components you'd find in a typical PC/Mac.
A static electricity shock so small, that you wouldn't even feel or notice it is all that it takes.
But................
That said...I've built 4 computers, standing on carpet (had sneakers on, though) and nothings ever gone wrong. However, I keep everything in a static bag until ready for installation. I also touch the powersupply/case chassis before handling anything and try not to move my feet while doing it. Sounds hard, but it becomes habit and you do it (don't do it?) subconsciously.
If I'm cleaning inside the case and remove anything, I place it in a static bag until it's time for reinstallation then I follow the steps above.