Window Mobile 6.5 was a visual upgrade over all else, which makes the fact that the new UI isn't very good particularly disturbing. Windows Mobile 6.5.1 takes the interface changes deeper—like they should've been in the first place.
Some of the especially jarring UI elements, like the Windows 3.1-esque radio buttons and aging contacts app, have been given a bubbly, antialiased skin, which, like it or not, is at the bare minimum less retro than what was there before. The start menu has been pulled from the top tray to the bottom menu, and the formerly text-based contextual buttons, present since 5.x, have been awkwardly iconified. If 6.5 was elective plastic surgery, 6.5.1 is a new suit.
Microsoft's given no indication as to when 6.5.1 is due to ship, or what the final product will look like—a while back I posed the question to Robbie Bach directly a few weeks back, and it was immediately deflected. Even more to the point, there's no guarantee that it'll ever come out, and that these aren't just escaped beta-chunks, slotted into cooked ROMs by eager homebrewers. Even if 6.5.1 shipped tomorrow, though, to the WinMo fans who've stuck it out this long, it'd be a pittance. [IStartedSomething via Download Squad]