When is Google information updated?

Like cached page, PR, backlinks, etc. Or are the "updates" really dead?

[MatthewHSE]

I've heard around here that the old-fashioned Google "dances" are essentially a thing of the past. But then, I've also seen some discussion about the backlinks and PR being updated on a schedule of some sort. So, when can I expect, for instance, the cached snapshot of my homepage to be updated? Or, any of the other information Google collects about a site?

Googlebot is coming by my site every single day lately, sometimes twice per day, generating much more bandwidth than it ever has before. And yet their cache of my pages - the standard I've been using to determine when they "update" - is several weeks old. I've done some basic SEO over the past couple of weeks, and am anxious to see what effect that has on our rankings. Any idea on how long I may have to wait?

Thanks,

Matthew