There are two things that will get me to upgrade my 3G iPod: Bluetooth support or a 10+ GB drive in the "Mini" form factor.
Well, it looks like I may not need to wait for the next-gen iPods for this - AirLogic has announced a Bluetooth dongle for existing iPod devices. Imagine being able to transfer songs between devices without wires or a computer. Imagine being able to listen to music while your player sits in the bad, and even being able to control the music with a built-in remote. Imagine real "podcasting" - that is, "broadcasting" your playlist to others sitting on the train.
In related news, Toshiba recently showed off a new 4GB player with Bluetooth support (also notable as the first player using Toshiba's 4GB 0.85 in drive). Engadget said "it looks awfully cumbersome and clunky for something so small" - but then, is that really a problem with Bluetooth support? I mean, it's never going to leave my bag anyways!