In reply to:
I understand the upgrade one-click might be tricky, but it would be nice if they could provide a new 1.5 install quickly.
I agree that would be nice, but I would rather have them go slowly and "get it right". 
I'd also recommend holding off for at least a week or so to "let the dust settle" as the first "stable" release of Joomla! 1.5 gets installed by others who can identify and report any "gotchas".
Joomla! is a *great* piece of software, and I have a huge amount of respect for and confidence in their development team, but I *always* believe it is best to let others "test" the newest releases before I commit my sites to the new code.
More than once I have been spared considerable grief by waiting for the "follow-up" bug-fix release that often follows the release of a new version.
Having gone through 4 release candidates, I'm hopeful that Joomla! 1.5 stable is "solid", but I'm waiting to hear that confirmed by other users before diving into what appears to be more of a "migration" than an "update" or "upgrade".
--rlparker