This has been an absolutely fascinating thread to read. I'm a little late to the party but I have a few comments about Android's UI. At first I thought UIexpert was trolling (there was a poster on Engadget named uiexpert who trolled vigorously), but he made some points that I begrudgingly agree with. Most of us are experienced Android users who have become acclimated to the OS's quirks and limitations. Sure you eventually learn Android, but there is a learning curve. Perhaps Google could make the UI a little more standard throughout the various system applications. Perhaps the manufacturers recognized this and decided (with varying degrees of success) to supply missing features through proprietary software (Sense, MotoBlur, TouchWiz, etc).
I've been using HTC's version of Android (Sense) for over a year, starting with the Sprint Hero and currently on the EVO, and I like it. I recently purchased my sister a Nexus S, and it was my first exposure to stock Android. It was pretty jarring. While stock Android felt noticeably zipper than Android + Sense, I thought stock Android was so ... spartan. It lacks features that even my Hero had (namely power control widgets, and other shortcuts). For example, on my EVO, if I want to enable/disable my mobile network I just tap the "Mobile" widget on my homescreen. I couldn't find a similar solution on the Nexus S. To do something as simple as enabling the mobile network on the Nexus S, I had to wade through layers of the settings menu. My sis figured it out after I showed her, but she probably wouldn't have figured it out on her own. And she shouldn't have to. I don't think customs skins are going anywhere anytime soon as long as the underlying UI remains so sparse. Maybe stock will grow on me, but not until Google adds more built-in widgets, options and shortcuts...
Also, no Android phones come with file managers (AndroZip, Astro, et. al.) built into the UI. I think future iterations of Android should have a stock file manager. Android should also explain the file folder structure, either through a tutorial or an instruction manual. I had no clue that I could manipulate my files without plugging my phone into a computer, until I stumbled across AndroZip in the Market.
I think this is an important, informative thread. I've learned alot, and I've enjoyed reading all of the back and forth. Often, real growth comes from critical self analysis. I think we Android users shouldn't be afraid to criticize the OS, when criticism is warranted. I love Android but it could be a bit more accessible and easier to understand for the non-techie.