I like to use the USB Mass Storage setting. This will bring up two drive letters on your PC. One will be sd, the other sd-ext. So far the internal sd gets the first new drive letter, sd-ext gets the second. sd-ext is where I keep my music and pictures. Create folders called "Music" and "Photos" and/or 'Videos". Drag your media to these locations and you should be good to go. I am not 100% on whether the phone will rescan immediately, but certainly a reboot will get you a rescan so the music and photos will show up. One thing stupid about the native gallery is that it will not recognize any directory structure that you may have set up in the photo sub-directory, you have to manually recreate folders in this app. I am using Gallery 3-d from the market which is nothing more than the old gallery application which will create and display photo subdirectories if you set these up when you move your photos to the card.
And I agree, this new system is very cumbersome at first. But I am guessing having the 4 switch settings is better if you know how to take advantage of syncing, etc.. I am a drag and drop kinda guy