Stuveltje - the difference is that toolbar PR is up to 3 months old (its just a snapshot of PR taken when Google feels like it and put into a database to show on the toolbar)
The "live" PR is what some people think is what Google has as the PR for a page "today" (or within the last day or so) and is what is used in the daily updates Google does now.

As far as whether it makes a difference which you use - my question has always been - why worry about it because it doesnt have very much effect on your ranking for keywords, and it has very little use to know what the live or toolbar PR is - because they dont gain or lose you anything.

I guess my question to you Stuveltje is - why would you care what the PR is of a page? Is someone basing link trades on it? If so I would run the other direction because they dont know what they are doing.

well i will tell you why i wanna know what the pr is and i dont wanna know what the pr is from an certain page, i wanna know what the pr is of my pages, in those almost 5 years i am in this bizz "pr" was always mentioned on every board and anywhere and everyday, some put huge valua to it other dont, i do know an pr1 site can get as much traffic or even better traffic then an pr5 or higher site, i also never had problems to do linktrades with newbies who had an pr0 site to trade with my pr4 or pr5 site ( and still dont have problems with that because i still trade my pr5 or pr4 links with pr0) even others told me not to do it because i would drop in pr.
it was always hell for me to check pr, as an newbie, pr talk was huge, well finally i got a year or 2 years ago my toolbar working , btw linkster if you remember you helped me with the toolbar set up from google because that damn thing didnt wanna work at my side. now i always check my pr i have alot of domains and yeah i am that freak who wanna know if i have still my pr , raeson i crosslink my sites and it helps to get my other sites an pr or listed in google,now the last days my stupid google bar was showing an certan time of the day no pr or a very low pr, so i thought i fucked up something because i work on several domains to make them better, i thought the damn thing was broke, so someone gave me the an new url and there i found the live pr thing and thought what the fuck is that, that was the only reason why i asked it on the board, if i dont understand a thing i will ask, i am not english, we learn new things everyday and i never saw live pr, so thats why my post about it

LOL - Stuveltje - I remember that :)
One thing to keep in mind is that Google is conducting a huge infrastructure change right now that is affecting all types of pages out there - it is supposed to settle down here in the next few days, but they are completely changing the way they handle queries and the way they index things.
The reason you may see that problem is when your toolbar hooks up to Google it tried to go to the most available server - and it isnt always the same datacenter - so some times you will hit a center that doesnt have the data - if you want you can always go to your hosts file and add a line to add in the IP of the datacenter you want to hit every time with your Google queries - but that would take all the fun out of watching pages in Google :)

ha well that explains, i had an other pr checker and that one showed pr0 for some of my pr4 in google toolbar and i thought what the hell is going on, i know now after your posting its google itself, but i realy thought, oke i fucked up and google toolbar is broke,now i see everyday an certain moment that my google toolbar is going nuts and i dont watch it anymore, i thinkt thats the best way:)