I'm getting a little cocerned here as this is the second time I've agreed with Paul this week!
The advantage of the proprietary stuff is principally their inheritant portability. It's easier to take a swig from a bottle than fish in your back pocket under race conditions. You can even (possibly) make a case for them on a
hard training ride. Other than that they are over-priced, over-processed, over-packaged and taste yuk!
I think one take home message from the seminar was the carbo content etc of real food and I'd always recommend something cheaper and better tasting before and after a ride and also during any ride where you have easy access to your back pockets....
Hence Paul's earlier referal to his minimalist "powerbar budget"...