I know that droplets created under 3.0 don't work in 3.5. I've had to recreate presets in 3.5. One thing that 3.5 added though is a neat little feature that might come in handy for you. If you have a file that's been encoded, you can drag it to the preset window and it will create a new preset based on how this file was encoded (for the most part). You may have to tweak it slightly, but it's pretty good. I don't know if you can drag an old droplet in there, but that might be worth a shot.