How often do your reinstall FS9?

I've just reformatted so too the opportunity to do FS9 again. I kept the old install, which had 250 Addon Scenery airports already installed and renamed itFLIGHT SIMULATOR 9 OLDThen I installed a fresh FS9, updated to 9.1 and IMMEDIATELY made a copy for fallback purposes.FLIGHT SIMULATOR FRESH + 9.1Then I just grabbed my old scenery.cfg and adjusted it to point all the files at FS9 OLD/Addon scenery folder. That sorted, I still has to copy in the 4 gigs of AI and all the other textures, since you can't alias that stuff from another install like scenery. It takes maybe an hour and is worth it.Some bits DEMAND re-install, like Activesky and Walk and follow, as well as the PMDG planes.Max.