I uploaded a rainlender skin (emanon) about a minute ago. Everything went very smooth. I experienced exatly what Dark Star said using IE 7 in XP. Mask was not very noticable and might confuse people.

FOLLOW UP- Thumbnail in the preview gallery is borked.
Trying to upload a wallpaper to my personal gallery resulted in the following. I am sure the details for uploading were correct since I goofed the first time. (emanon1280)
Your skin has failed to upload.
Error code: UploadDetails
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