I wouldn't say their bookmarklet is "lightyears ahead" of Tumblr. I'd say it's anything but. Tumblr's can do all of this, plus it doesn't try to autoguess what information you're trying to slurp off the page. It's far more user-friendly and makes more sense than Posterous's.
I have been waiting for a Posterous bookmarklet for awhile now, but this one missed the mark for me.
Seems cool and all, but it wasn't interpreting dates and times right for me. I said "Meeting today at 6:30pm" and it's telling me that's 22 hours away from now. I said "Meeting with Andy on 1/30/09" and it put it on January 12th. Clearly some issues here.