I bought a standard JR pass for Oct 2009 and had no problem going from Osaka to Sapporo. I would suggest not going from Tokyo to Hokkaido in one stretch, but break it up along the way. I went from Omiya (just outside Tokyo) to Aomori and spent the night there. Trains tend to get no-so-nice the further you get away from Osaka and Tokyo, so the Shinkansen from Omiya to Aomori wasn't as nice as the Shinkansen from Osaka to Tokyo/Omiya; and the train (no Shinkansen is available) from Aomori to Sapporo was very basic and not even as nice as the local trains you get from Osaka to Kobe.

I would highly recommend buying the JR Pass, because they're also good for the JR ferries and JR Highway bus. I took the JR bus to Oirase Stream up in Aormori and then hopped right on the JR train when I got back into town without any hitches.

Keep in mind you have to activate your JR Pass before you use it. If you're in Tokyo (or any other major city), you might want to do it the day before you use it, because of the lines at the major stations. Also, pre-book your seats if you're taking a busy line or you may not get the exact time you want. Usually this isn't a big deal because trains are so frequent, but as you head north, trains will become less frequent.

Check out the following link for train schedules and travel times...www.hyperdia.com