Startup items no longer load in Lion
Looking in the console log is the first place to look for launchd errors to debug the process. 

I use Lingon to look into the actual launchd configuration files - it automates finding the files and editing the plist files. 

You can look in your (now hidden) ~/Library/LaunchAgents  directory to make sure the items are enabled. 

Lastly ( or perhaps firstly ) try deleting all the items from the account pane, reboot and add them back to see if that helps.