This. Today was something of a unique case, though--servers were very wobbly for whatever reason while they did their maintenance work. Either going into offline mode or simply closing Steam and restarting it, even in online mode, fixed the "preparing to launch ad infinitum" issue that's been going on today.
I've had times where Steam wouldn't launch Skyrim. I usually just restart my computer, and that seems to work for me. Or you could try using self-replicating Briar Hearts...
If you don't know what I'm getting at with the replicating Briar Hearts, type "Briar Hearts multiply," "Briar Hearts overencumbered," or something similar in the search bar, and you'll find what I'm talking about.