Are you charging on... your computer or just in a power outlet? It could be as simple as that.
Otherwise, it could be driver support, but the Droid is automatic plug and play on windows so it should appear automatically. We'd probably need a few more details to figure out what exactly is going on. Anything from your USB port to software problems could be the culprit. Probably not something with the Droid, though.
As far as I know mounting has not changed at all. Do you see the little USB icon on the top left of your phone?