For starters, have two areas based on versions 1.0 & 1.5 so those looking for 1.5 compatiable can find it quickly, amazes me nobody thought of this.
Its hard enough that we have to sift through many pages looking for something (especially for compatibility) but then we have to view the commercial extensions as well which take up my time, personally I feel offended that they are even mixed in the first place, there sure are lot of joomola $$ seekers trying to sell you their expensive stuff, sometimes I wonder if certain extensions are intentionally rigged to fail so they will get you to pay for the one that works.
Joomla being open source, I would expect all extensions to be non-commercial then in another location, you can have the commercial stuff, I think wordpress does something like that, its annoying seeing an ad every where we turn in joomla.
I also find Joomla commercial extensions to be quite expensive, wordpress you find them much cheaper like $10-$15 (reasonable) no way in hell I'd ever pay $50-$100 for a silly pice of plugin code but that's just me. Donation is the way to go, if your code is that good people will pay within reason.
Another thing, there are many of the download pages for the extensions direct to another site which requires you to create an account just to download, very bad idea, I refuse to have to create an account everywhere I go, its silly. When I do i just use disposable email address and fake the rest, the things we have to do just to download something, I think these improvements would make the joomla experience way better and I also think many would agree, just my valuable 2 cents

oh and why do we have to create another account for the extension area ? is this real ?
many times I wanted to comment on an extension but I couldn't without having to create another account, please say it ain't so, login should be accross the board for all Joomla