Yea one of my sites was PR0, and it jumped to PR4, then to PR5, now it's back at PR4. In regards to the "prediction tools", I have had some moderately good experiences with them. I know they are not anywhere close to 100% accurate, but I have noticed that when the tools indicate a drastic change in PR you can expect to see something If i'm not mistaken iWebtool has a % with its predictions also.
Prediction tools are horrible, everytime it tells me pr3-pr4 and it never happens. My advice is just to not worry about pr and build links/market.
Taking a site down is only going to make it harder to get the PR (let alone visitor numbers) back up...
the thing was though.. i only got like 10 hits to my main page a day and like 100 or more to my forums.