There's a lot of factors in there, one major one being who's linking to you & how often to those that link to you get indexed & how far do they get indexed.
An example is if you build a free site & submit it to 8-10 link lists with decent PR's, you'll see some PR on your page in about 30-60 days (maybe sooner, depending on the spider's time frame) This does me that Google knows your out there, but does not mean you're listed.
It's like a never ending mad cycle
