If you were dropping into the single digits, you would have something to worry about. If your first entering a cell, the game has to rev up all it's scripts, so if your measuring frame rates at cell load, they will drop. NPCs will cause the game to slow down as they are the most script intensive, that is why there are not more of them. Most people clamp the game to 40 to 50 for butter smooth play. This masks the FPS drops that occur and avoids the issues that you can get when running the game at 60 FPS.
One thing that helps is, weirdly enough:
Turn off the gamepad rumble in the prefs file My Documents/My Games/Skyrim, find this line and make it look like this:
bGamePadRumble=0
I don't notice these drops at all, but I also have a mod that tells all the NPCs to ignore me unless I speak to them, so perhaps my script load is less than normal (I doubt it, I think it is more the frame rate clamp) Also, make sure you have the unofficial patches, for the game and the DLC, it does optimize some scripts so the game runs better, but mostly it fixes a lot of bugs.