Leopard’s “Stacks” does NOT presently support custom stacks made from files all over the computer, nor does it support “smart folders” made of, say, all the downloads made by the web browser, no matter where they ended up. Also, at present, stacks look extremely messy, being just a “pile” of icons. There’s a third party hack that puts a transparent glass “tray” over the top, providing a symbol that tells you you’re looking at the Applications folder and not the Address Book (which will ordinarily be the icon on top):

http://t.ecksdee.org/post/19001860

However, this fix is unofficial, and 10.5.2 only lets you view the folder icon instead, which is a bit backward.

By including a feature with these enhancements, Ubuntu could legitimately claim to have innovated on the Stacks concept.

Admittedly, Ubuntu has a library of stunning third-party themes and hacks to improve its visuals, but the default look is the first thing people see, and at the minute, Ubuntu’s default theme looks like a case of “pay peanuts, get monkeys”. If the concern is that a new theme would damage Ubuntu’s ability to run on older systems, it shouldn’t be too hard to include an option at install to load the “classic” or “enhanced” theme as default.

I would also like to see the Ubuntu and GNOME teams attempt to match Vista/Leopard’s features (at least in potentia for third party themes), as at the minute the commercial OSes seem to have pulled ahead:
- True translucency (as opposed to a transparency + blur hack) with an animated gloss/shifting sheen as per Aero Glass.
- Smooth rollover button effects as per the Vista start menu and title bar buttons.
- Reflective surfaces as per the Leopard dock.
- Support for a Stacks/smart folders equivalent (a good place for Ubuntu to pull ahead - stacks which represent files from more than one folder, stacks created from Safari downloads, a “tray” in which the icons sit, identifying the stack without having to scrub over them with the mouse).
- Support (for those with sufficiently powerful graphics cards) for themes utilising full vector graphics as per both commercial OSes (at present Ubuntu I believe is stuck with raster).
- Different desktop backgrounds/icons/shortcuts on different workspaces, with the ability to rename workspaces, as has been available on KDE for ages and has now been hacked into Vista and even XP.
- Live previews of other desktops and minimised windows, as per KDE and Vista. Looking Glass has a very nice feature where minimised window appear on the dock equivalent turned slightly sideways. Scrubbing over them makes them turn towards you, rise, and expand, so you can make sure it’s what you want in much better resolution than OS X/Vista.

Another priority should be PROGRAMS. With Office 2007/8 available for both Windows and OS X (and virtually impossible to get working under Wine), Ubuntu has been left firmly in the dust. With no OpenOffice (sorry, “Openoffice.org” or “Ooo” - seriously, they need to rebrand their product) update any time, might it be worth setting up a team to produce a suite of Linux-ONLY programs (office equivalent, video editor, graphics program, backup, etc.) with interfaces and functionality that showcase the superiority (we still believe that, right?) of open source. The hope would be to score a “hit” like iMovie or Microsoft Office that becomes the industry standard in some field, which would massively raise Ubuntu’s market share.

At this point in the art process, I don’t think any of this is specific to Ubuntu, as opposed to Kubuntu, even though many people used the gnome desktop for their mockups. Correct me if I am wrong, though.