I think early access is a different situation from preordering, since the former gives you something right away, and that something is one which you can influence as a tester.

I've generally been pretty gung-ho with early access games if they have a Linux/SteamOS version available. Kerbal Space Program and Planet Explorers have taken weeks' worth of my time (and that time was enjoyable, even amid the bugs; in fact, the bugs were part of the reason why I enjoyed them). With both of those games, I had a chance to experience their evolution from alpha-quality-at-best to finished product. That's not an experience normally possible in the release cycle of a non-early-access game.