Or if you want a more authoritative page on PageRank, you can hear it from the "father of search himself, Danny Sullivan.
In any event, with regards to your question, as stymiee said, higher PageRank pages get crawled more often, but also, if you update your content infrequently, it will also likely be crawled less frequently.
Without wishing to contradict either your amazing self or the father of search PageRank has no direct relevancy with crawl speed. In much the same way as
PageRank does not equate to rankings. However there is a correlation between crawl speeds and PageRank and PageRank and Rankings (say that three times while drunk!).
Google crawler arrives to the site via inbound links, if you imagine the web as a pile of long corridors with doors all the way along, each door goes to another corridor with yet more doors then you have a good image of how the web is seen by Google. For every new door (link) you create the chance of Google attempting to come through a door to your corridor increases. Now some doors are locked noindex but allow Google to peer through others are completely barred.
For your site to be crawled and ranked quickly your first port of call would be links the more the better this is why
people associate high crawl rates with high PR as they both have a very large factor in common inbound links but this is not the only way.
Blog posts particularly on established domains are crawled at very high speed without any real external links they do this through a process of pinging. When the post is published the site sends a message or ping request to blog search engines, the exact engines will be based on how the site is set up. Some sites like Technorati will then add a link back to the post almost immediately, as Technorati has many doors to its site it is crawled very regularly giving your post a good chance of being spotted. Google also has the advantage of Google Blog search which is a dedicated system for blogs (strictly speaking anything with an rss feed) which crawls just the post when pinged and adds it to its index. The main search engine appears to use the Google blog search index while it waits to do its own crawl.
The result many pages on regular sites are found crawled and ranked by Google within minutes of posting.
Couple of other things as Tamar has already stated the frequency of posting can effect the crawl rate so if you haven't posted to the site in 3 years expect Google to have forgotten and stopped looking through your door, you can also suggest a priority of a page in your sitemap and use the robots.txt option to allow your sitemaps to be auto discovered by major engines and ping them. From personal experience the priority within a sitemap is ignored by all but Google and then only on large sites.
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