I assum compatibility issues download hd themes for 4.0 bg folders and multitasking can't be themed just like that for theme them you neet ssh and re-name
you can theme the folderswitcher by getting iwipe cache from cydia, then go to system/library/coreservices/springboard.app and replace the folderswitcher with your own image..
then in ifile open iwipecache's payload (var/stash/applications/iwipecache/run) and before the KillAll SpringBoard add this
rm -rf /private/var/mobile/Library/Caches/com.apple.SpringBoard.folderSwitcherBG@2x
then save and open iwipe, your device will respring and it will have wiped the cached image for folderswitcher, forcing it to fetch your image!!!
as for your themes not working itll be down to the themes not being updated, winterboard (generally speaking) is fine..
iPhone4 16gb black - 4.1 Limera1ned
iPhone 3G 16gb white - 3.1.2 jailbroken Blackra1ned THANKYOU ONCE AGAIN GEOHOT!