Over 20 times since January 2008. Usually from OS 2008 to 2007 or visa-versa, just for the applications available in one that aren't ported to the other. Though I've been sticking with OS 2008 lately.

The last time I flashed was a few weeks ago from OS 2008 to 2007. But after installing a bunch of Bora apps and being disappointed with not being able to install some Chinook apps (Evince, TiEmu, Basilisk II, all the neat GUI modifications, etc.) I reflashed back to OS 2008 within 2 hours.

Now I have 6 MB free on my N800 and looking to clone it to a SD card to have more free space for applications.