It really does not useful to end users. The PR what u see on tool bar may not be very correct with the what google search has it..
Google toolbar is a tool which provide us details like catching PR and all but some time it does not show the correct PR may be that is why you got confused...
the pr is the thing that is checked the google toolbar is a tool that checks it. there is a difference.
"Real" PR and Google Toolbar PR are VERY different things... They don't use the same numbering systems. "Real" PR is CONSTANTLY being updated while Toolbar PR is never current... Google's Toolbar PR is ALWAYS out of date even the VERY DAY that Google publishes an update to the Toobar PR. "Real" PR is used by the ranking algorithm... Toolbar PR is NOT used by the ranking algorithm. The list goes on. Perhaps this explanation from one of my previous posts will help: