When the client is first started on my wife's MacBook Pro, running 10.5, it appears to work, until it starts trying to update. I get a window that complains about errors, asks if it should abort "Yes No Cancel, click cancel to suppress further errors" Clicking yes, obviously aborts the update.. Clicking No just brings the window right back again, clicking Cancel makes it go away..
However, at that point, nothing is updated. Oh, sure, the windows all pop up in the bottom right corner, but everything says "Failed" and then the addon list is empty.
It's done this on every single version I've tried.. And I've tried it off and on since Valentine's Day (Thats when I bought the wife the MBP). And it did the same thing yesterday afternoon, after letting the client update itself to the latest Mac version.