Organizing skype downloads in subfolders with contact names
So I made a script and saved it as a folder action:

for f in "$@"
do
    userFolder=~/Downloads/Skype/`xattr -p com.apple.metadata:kMDItemWhereFroms "$f" | sed -e 's/0D//g' -e 's/.*\(5F 10\)...//' -e 's/00.*//'| xxd -r -p | sed -e 's@ (.*@@g'`
    mkdir -p "$userFolder"
    mv "$f" "$userFolder"
done


What it does:


gets where from field from file. In binary
deletes some binary-plist prefix
delete nulls at the end
creates string from binary with xxd
Gets the name of the contact from string.
creates a folder for that contact
moves file there.


If you have more elegant solution, I would be glad to see them :) 
P.S. if you didn't know about where from filed you can find it in get info for some finder items.

To categorize existing downloads you can also add service.