No. If the update comes to you, just update. The worst that may happen is the adw launcher will get squirly. In that case, uninstall it and then reinstall it. I did the manual OTA GB download couple months ago and had to do this with Launcher Pro Plus. After I did it, all was fine. You might find several apps that need this same procedure after the update. But, don't panic. It's designed to be as stress-less as possible.
However, just know that all your dl apps may not work with GB. Only after it's downloaded will you know for sure. Most apps, especially at this point with GB already in use as a leak, most apps are compatible. Would pay to make a list of your apps -- paid and free -- just so you can check up after the upgrade. Market will download (for no additional charge) any apps you have purchased in the past,