Google's ranking system is a closely guarded secret. Sure, the company lays out general guidelines and reveals the factors that go into determining a site's relevance, but knowing the exact algorithm would be worth a lot of money to a lot of people. That's not going to happen anytime soon, but something that will happen is including page loading speed as a factor in the organic ranking algorithm.
This comes straight from one of Google's top engineers, Matt Cutts, so it's not a question of if, it's a question of when. And the answer is 'as early as next year.' The reasoning is that faster pages make for a better experience, so they should rank higher. With speed-obsessed Google, it's a surprise that it hasn't introduced it earlier.
"Historically, we haven't had to use it in our search rankings, but a lot of people within Google think that the web should be fast," Cutts told WebProNews. "It should be a good experience, and so it's sort of fair to say that if you're a fast site, maybe you should get a little bit of a bonus. If you really have an awfully slow site, then maybe users don't want that as much."
It's no reason to worry yet, even if your site may be a little sluggish. It's still going to be a while until Google makes the changes, and, even so, speed isn't going to make that much of a difference in the vast majority of the cases. Google takes into account over 200 factors when determining ranking, so adding a new one won't affect the system too much.