There are many reasons why you would get the notification. The most likely are:
-you still haven't gotten the MR update (the most likely)
-you are using a custom rom based off of the stock UI and are getting false notifications
-or it is an android update (this is what you are hoping for)
Only way to tell what the update is, is the software number of the update. when you do it look for the android version number and software number in the about phone settings menu (menu>settings>about phone>software information). If its froyo it will say:
Android version 2.2.1
Software version 2.13.531.1 or 2.15.531.1 (these are the two software versions of froyo for the slide)
Since it is likely just the MR release you should see:
Android version 2.1 update1
Software version 1.35.531.1
Though it is not likely that you received the OTA as it has not begun officially going out to devices, the update is in fact on OTA servers ready to be pushed any day now. Let us know what software you are on after you complete the update.
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