Get the trial, I'd say. But honestly, starting right now probably isn't a great idea; the vanilla content is a complete ghost town these days, because no one wants to level a new alt before Cataclysm launches.
Once that comes out, you'll probably find it a LOT easier to find groups, join a guild, and generally meet a bunch of cool people.
EDIT: Also, as you might've gathered from some of the above posters, it's possible to get really really addicted to it. It depends on your personality and circumstances. For example, I can normally put it down and walk away for a few weeks (or months) without any problem, but I did have a pretty bad period of addiction for a couple of months after I got laid off from an old job. So be warned.