Hi Daniel,
Google indexing and than PR take both a bit of time.
First you will get indexed, than based on the information google collected you will get a PR rank.
It is good that you have sitemap in place and also that you had the opportunity to have some posts on some fairly large blogs.
Google webmasters tools takes a while to update the info in the dashboard, however the bot is active on a daily basis.
Google PR is updated if I am not wrong 4-5 times a year. I know one updated was in April, another one June ... so I would guess that a next one should most likely be in December or January 2008.
keep posting, build links and when PR gets revised and assigned you will have a nice surprise.
Anyhow, PR is just a measure of the popularity and authority of your site and will not determine any thing else.
Content, crawl frequency and quality of posts is way more important.
I suggest (if you use wordpress) to check out the All-in-One SEO pack plugin which is a great way to optimize your blog from an SEO perspective.
Good Luck,
Alex