I've got an MT installation that's running two separate blogs.  Right now, I'm simply using the <MTDate format="%m.%d.%y at %I:%M%p" lower_case="1"> to display a "last updated" date on my archive page, but the problem is that it shows the most recent date of whichever blog I last updated... is there anyway to show a "last updated" date specific only to one of the two blogs?

You'll need to use MTEntryDate instead of MTDate.  It would look something like this:

Interesting. MTDate returns the date the page that it's displayed on was last rebuilt, not the date you last updated any blog.

The tag can't be updated in the archive page unless the archive page is rebuilt, so what you're saying doesn't make sense. If you rebuild blog A, a page in blog B isn't going to be rebuilt at all, and therefore, can't show blog A's last updated date - unless you've also rebuilt the page in blog B during the same step. I don't quite see how that could happen.

Or are you maybe using the MTDate tag in a sidebar which is being included in all your pages via some sort of server side include?

here's an idea.. put php code in both blogs in the MTDateHeader area to write the date to two seperate text files , and then just reference those files?

I dunno.. newbie talking outloud