Totally pointless unless...

a. You're having problems.
b. You use a lot of software from the testing or development repos.
c. You just get a kick out of having to redo all your customized setup.

None of those apply to me. So unless something changes I'll probably never reflash as long as I use the N900. I got one of the 1st G1s, used the heck out of it and have still never reflashed it. It runs like new. I reinstall my linux desktop only every few years and may not reinstall linux 'til the distro's EOL in 2014. Even with Windoze I almost never reinstall the OS for the life of a machine. I have one 8-year-old Win2000Pro machine in our office still running the original install perfectly. Some maintenance, common sense and if necessary, a little trouble-shooting can save a lot of setup time.