Dieter rates this rumor at 10%. He may be generous. Never-the-less, noted Silicon spysite Valley Wag is reporting that:

A source who's plugged into the Valley's deal scene and has been recruited by Apple for a senior position says Apple and Twitter are in serious negotiations, with the goal of unveiling a deal by June 8, when Apple's annual Worldwide Developers Conference launches in San Jose.

Valleywag thinks Apple may want to uber-cool web savvy of the Twitter crew for their own. Dieter had another idea: what if they're looking to spice up a BlackBerry Messenger (MMB)-style service to compete with RIM?

Of course BBM is completely proprietary to BlackBerrys and BlackBerry Connect, while Twitter is pretty much as open a messaging platform as can be, still Apple has been known to weave amazingly slick proprietary versions of software that they, or others, leave as open at its source. (CalDAV, CardDAV, etc.)

Don't think it will happen. But can we imagine what, if anything, Apple would do with Twitter if they did acquire it? Could they do worse than Google's done with Jaiku so far?