Yeah, I did also (in fact, I actually used Clonezilla to back it up too!).
But from what I have read, Microsoft actually deletes your license of Windows 7 after 30 days. So if I reverted my computer back to a saved image, I would be scared that Windows would want me to buy another license. Since I don't use that computer much, it wouldn't really be worth it.
Dan
I wouldn't think your license would be invalidated. That would be absurd on Microsoft's part. However, it will still be tied to the machine originally installed on. I ran ProduKey on my Win10 intstall and it still has my key listed as Windows 8.