It's no secret: bandwidth issue is severely degrading performance lately on WinCustomize. So I told to myself: What could be done to "patch" this issue since buying bandwidth is *very very* costy. Here's what I come with. (Btw, sorry for my lack of english vocabulary. I'm a french speaking guy so I'll try to do my best to explain things clearly).
I've noticed there's no filtering on submissions file size. Whether it is a zip file or a jpg thumb, my "investigation" showed me there are important differences in file size which, you can easily understand, affects bandwidth availability.
Let's take for example thumbs in the Wallpaper section. They're all the same dimensions but file size vary's a lot. Ok, jpg compressions takes into consideration # of colors and stuff but from my own tests, some thumbs that weighted 40KB could have easily been compressed to half their size with barrely noticeable lost in quality. You may say: Hey, 20 KB less is no big deal! But consider that if 75,000 users comes in and see this thumb, 20 KB less means we save in bandwidth 75,000 x 20 KB = 1.5 GB a day!

Now take this result and apply it to every zips and jpgs that floats around WC (coz remember, the previous result was for a *single* thumbnail!!!)... Now I think you get the picture.
So my suggestion would be to thighten the rules around submissions in terms of file size and format (BMP vs JPG in zips, thumbs file size, etc.). Details of what could be done is up to the admins of WC so I won't get into it (although i'm open to chat with them about it). But for sure, something has to be done for that aspect, IMHO.
Hope this help. Ciao all!