I am rather anal about how I download and install stuff. I have a big downloads folder on my second hard drive, inside that I have an Unused Downloads and a Used Downloads folder. Each is then subfoldered by site. So, if I download a set from ATS2, for example, it would first go into Unused Downloads/ATS2. When I've finished downloading, and I'm in the mood, I start unzipping all this stuff, adding pics that I always download at the same time, rename the unzipped folder from whatever long and involved name it has to just the name of the set, copy that name to the pic, then unzip a second time within the first folder, chuck the zip into the recycle bin, and move the contents of the second folder over to my Downloads folder if I want it in my current game. If not, it just stays put until I do want it. (Oh, and if a set includes walls and floors, I sort them out into their own folders etc. too!) If I've put the stuff in game, I then move the remaining folder to Used Downloads/ATS2, and eventually it gets backed up to CD and even then I keep the copy on my PC, now in a subfolder called Downloads saved to CD/DVD!)
And if you're wondering why I'm so obsessive, about 18 months ago my hard drives both got fried by McAfee and I lost EVERYTHING!