The nature of phone and mobile operating systems means that there is a bit of a delay from when Google releases the latest version of Android, and when that update makes its way to all the various phones. For one, the operating system and related files has to be built specifically for each phone, and there isn't just one copy of the OS that gets distributed to all devices. This is something that has to be done by the device manufacturer, and not by Google. Even if the manufacturer uses the stock version of Android, this introduces some delay, as the drivers have to be updated, quality testing has to be done, etc. Also, many device manufacturers add their own UI or other features on top of the stock Android OS, such as the MotoBLUR interface on the Backflip, and this code has to be modified to account for the new Android versions. Furthermore, carriers will introduce their own delays in this process, as they have specific requests such as carrier applications (ugh) and their own quality assurance process. In all this ends up accumulating to several months of work, especially for larger jumps like from 1.5 to 2.1, where there have been a ton of changes to the underlying OS. Luckily (in a way) the Android release schedule will be slowing down after the next couple of versions, with more stuff being modularized which should give the manufacturers more time to do their updates before the next great version is out.
Your best bet would be to keep an eye on this page: https://supportforums.motorola.com/community/manager/softwareupgrades
. Moto will update that with details when the update is imminent, which could be anywhere from 2 days from now (unlikely) to 3 months from now.