Everyone in here seems to not have good experiences with PR checkers. I however have been using them for over a year now and I am always pleasantly surprised when the results come. The PR checker usually predicts a PR2 or PR3 and my site will get a PR3 or a PR4!
Future PR checker can be a useful tool if they use the exact algo used by google to calculate the PR but google does not reveal it. That's the problem...