well i try a lot of different things new programs, or work on a new graphic its not really the work i do something like menu cards in 3 different languages you can always put that in a safe place

but if you change something on the system and find it works good after a time then i will back it up now it only makes a differential backup even if i have 1000 GB that you can use up quick NP i have a second computer where i store things that also works better than USB extern HD so to answer your question not very often when the system is running fine then i make one same with the boot menu i tried to do then i make one before saves a lot of time and with the OEM version you might have a problem to activate it

i haven't tried to save the wpa.dll with vista don't know even if that works. there are other ways Microsoft could have done it to stop a system being installed more times than just block it. I said that way because i had a lot of problem with my laptop with all the pre installed drivers and media edition and it took up the whole hard drive 100 GB and that wasn't my taste i wanted to split it up that was a job then a complete backup is much more efficient and safer