My site has a PR of 0 since it is a new site. I have tried some PageRank predictors that are offered by many websites. I keep getting up with different results, anywhere from a PR 0 to a PR 5.

I wonder if these PR predictors are usefull tools or shouldn't be taken seriously.

What do you think?

Not at all. In fact, the Google PR toolbar shouldn't be taken seriously, either.

The green bar on the google toolbar is quite interesting.
Many seos use it as a general indicator of page and site quality. some seos, including world famous Mike Grehan call page rank "green fairy dust" and preaches to uninstall the toolbar.

5 Tips / Uses for Reading Google TBPR:

1. Pagerank and TBPR (tool bar page rank) should not be confused with each other. True PR is a metric hidden from the public eye. TBPR is a murky figure only updated currently approximately once every 90 days more or less at Google's discression. It is a very rough measure / indicator of page quality.

2. Sites with GREY TPBR have been banned from the index. Many SEOs say that they use the TBPR meter for that purpose only (Thou shall not get links from banned sites!)! 0 TBPR is shown in white.

3. If a page has GREEN TBPR, it is most likely indexed by Google.

4. A page can be dripping wet with PR, and the TB will show a 0. It takes time for new sites /pages to get some green.

5. Sites / Pages that have low TBPR may still be quality sites! PR has almost nothing to do with keyword positioning / ranking in the SERPS. Focusing too much on the green is not the best SEO practice.

Green fairy dust, cute.