The domain usually loose PR after expiring, anyhow if there is lot of backlinks it gains its PR back. Anyhow it is perceived as new domain by Google and it has to fight with sandbox.
As Xaver mentioned most expired domains loose their PR. I have a couple that returned to PR5 after about 6 months though traffic has not returned! I believe Network Solutions treats their expired domains purchased at Snapnames.com as tranfers? I have a few of their domains that retained their page rank witout dropping. Though traffic has dropped to almost nothing for most (20-50 uniques per day)! These domains can be quite expensive depending on who is bidding!