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I think you're seeing what I would call "inherited" toolbar PageRank. Sub-pages of sites often see this effect - they "inherit" the toolbar value from a higher-level page, instead of being based on a calculation of that URL's actual value.
I don't think it's any indication of how much value your profile page is likely to pass to pages it links to. But then, this is broadly true of all toolbar PR data, IMO.
Still, you could always test it yourself by linking to something using desirable keywords and seeing whether you get PR9-style link strength. Uninitiated link builders might give you a fair price too ;)
Actually, I see that it depends on what toolbar I'm using and what route I've taken to get to the page in question. With one route in, the Google Toolbar gives me a PR9 on my FB home page and a grey bar on my profile page.
But if I navigate around a bit, the Google Toolbar in IE shows a grey bar on both my home and profile pages, whereas at least one toolbar in Firefox continues to show PR9 on both pages.
[edited by: Robert_Charlton at 5:15 am (utc) on May 7, 2009]
The linkage opportunity is quite limited, though, with the current profile page design.
So,there is no reason to get high PR.
The point is that it doesn't have high PR - it is simply based on a connection with high PR pages on the same site, that the toolbar misinterprets - hence my use of the word "inherit". It hasn't actually "inherited" anything - just an issue with the way the toolbar green bar works (and there is no connection with behind the scnes PR - which is about the real link value of a page).
It's a similar effect to the various methods of "faking" toolbar PR for a given URL that have worked over time. The toolbar is at best indicative and at worst totally inaccurate.
However, I have never seen such an issue with IE where the TBPR is queried before page is downloaded.