i think it's not accurate.My Pr now is 0.And they predict i get Pr 4. I never trust it.I think Pr 1 for me is better.
These tools have built in problem that they are fast in predictions while google is slow to set PR. At the end these tools cannot be accurate because they don't care about rationale data. I'll soon add pagerank prediction in backlinkwatch tool using its database to predict on basis of every counted link .. its PR and keeping regard of nofollow flag and outbound links
It sucks if you ask me! seobook.com and some other big PR 7 sites are predicted to be PR4 and PR3 everytime I check just their PR does not drop like the tools say it will.