Touch the notification and it will go away. Of course, this will re-enable background data.
The thing here is, it's meant to be annoying. Many of your apps use background data in order to sync themselves or receive updates, notifications or whatever from the network, and without it, they can't do that.
If apps do background data correctly then this can actually save you battery, as well as make the apps appear more responsive when you actually do open them up to see what they have to tell you. Unfortunately some apps don't, which is probably why you decided you wanted it disabled in the first place.
You have a few options. In order from easiest to hardest:
- You can live with the notification.
- You can remove the offending apps and replace them with less offensive apps.
- You can hack the Android source code to do what you want.