I agree with the other two posters. Unless you have a hard copy of a recovery disk I would keep the recovery partition.
While you may never revert back to Vista, if you are purchasing an upgrade disk, you will need to have an activated copy of a prior Microsoft OS on the computer if you ever need to reinstall Windows 7.
To my understanding if you needed to reinstall Windows 7 with an upgrade disk you would need to first go back and reinstall Vista. If you delete that partition and have no recovery disk you will not be able to reinstall Windows 7.
If you however happen to have a retail version of Windows 7 that is not the case. However, if you ever want to sell this computer and use your retail copy on another computer you would need to revert it back to Vista.