Well you know when you take apart the wii, there are like a bizillion screws and they are all different sizes. Well what I do to remember where they go and I don't lose them is draw a picture.
Yes I draw a picture of each side of the wii where the screws come out. Make it resemble that side so I remember which way it was facing etc. Then I draw a little circle to reference where I took out the screws from. Then I take a piece of double sided tape and place it on that little circle area and put my screws on the tape as I take them out. This way when I put it back together I will know exactly where the screws go. This really doesnt help to much though if you take the thing completely apart. This is just good enough to get to your dvd drive.
If you plan on swapping cases or something, theres alot of screws to go and its actually one of the worst systems I have ever taken apart. There is to many damn screws!