I'm a fan of DL and will upgrade. It suits our needs since some of our books, CDs and DVDs are here (China) and others back home. I also like the fact that you can keep the list on your iPod ... helps prevent duplicate purchases if you forget what you have.
However, the main reason I like DL (and certain other apps) is - and it was expressed quite succinctly above - that Wil Shipley and his team (as well as other developers of a similar calibre) are the ones who "hack through the jungle" for us. Their code is clean, tight and vanguard stuff - their implementation of new technologies is inspiring and that raises the bar, which benefits us all.
Btw, iirc, the update will be US$80 - that's double the original price.
I'm hoping that DL2 can also just pull all the stuff out of iTunes automatically ... seems a "given" - at least I hope it is.