What does/did Aero mean?
MS partially fouled this one up by using the term Aero too loosely in their marketing. When Vista was in beta, Aero clearly meant the windowing scheme, the layout of the Start panel, search in window functionality etc -- all of which work in 2D mode. Aero Glass (the full Vista experience) adds the 3D effects and requires a different video driver model capable of DX10. MS handily provided sample images that demonstrated overlapping desktop windows: with Aero Glass, the overlapping area was semi transparent, and with Aero it was "flat" as in XP. When Vista was released, it was clear that Aero =/= Aero Glass.
Vista Capable meant that a PC could run Vista. Most beta testers used virtual machines or machine room junk for their evaluation, experiencing the Aero experience. When they wanted to show it off, they installed Vista on a PC with a meaty graphics card so that Aero Glass was enabled. But even the machine room junk was "Vista capable" -- I ran Office 2007, IE7 and (heavens forbid) SMS client with Vista Enterprise in an AD environment on an Intel 845 board.
I have little sympathy with the whingers who claim that Vista runs slowly on the PC that they bought last week. If the OS does not work, blame the PC manufacturer. I've just booted Vista SP1 into a virtual machine on a three year old PC that predates the Vista launch: i'd be happy to use that VM as my desktop system.