Here are some points about the 30:
1. Huge range of flash functions : master/slave control, flash ratio control etc in a multiple flash setup. These features are only there on the EOS-3 and 1V.
2. An incredibly responsive eye controlled focus system. I gave up on my EOS-3, and the 50 was too slow.
3. A very accurate and fast AF tracking system. I feel it is as good as the AF tracking on the EOS-3.
4. True mirror lockup, like the EOS-3 and 1V
5. Dedicated DOF preview button unlike the 50E/50 which doesn't have one. The * button doubles as the DOFP on the 50.
6. Metal top and bottom plates - more robust than the 50
7. The quietest SLR I've used, including the EOS-5.
8. A really cool feature : you can program an external flash (or ST-E2) to emit the AF-assist but disable flash, or vice-versa.
IMHO, the 30 doesn't have one or two new whizzbang features - it is the combination of all these improvements which makes the 30 a great body. That's why I bought it.
As for the 50, the response is quite a bit slower than the 30, and the 300 is not programmable - no custom functions. I can't live without the film leader out and a few other functions
