Has anyone seen any benefits to using skins such as MotoBlur and HTC Sense as opposed to "vanilla" Android like on the Nexus One?
I'm considering getting the Nexus S and this is part of my pre-purchase evaluation.
I wouldn't want to call MotoBlur or HTC Sense just "skins" -- they aren't a suite of visual enhancements, but an entire app suite that sits on top of the OS. They're full-fledged graphical user interfaces with additional custom apps, virtual keyboards, widgets, etc.
So, as to the benefits? I like Sense - its my major UI on the Incredible, but I've also used my wife's Aria. The Sense UI is cleaner and smoother (hardware speeds aside). The custom widgets are smoothly integrated and have more features. Other than the HTC mail and messaging apps having a possible memory leak issue [I replaced their use with K9 and Gmail, and Handcent], I've been pleased with Sense. A smooth, consistent user experience with the interface can make using it better. It's not the be-all end-all -- despite the recent MS WinMo7 commercials -- but it's nice.
"Vanilla" Android devices (like the N1) usually mean that you wait less time to get updates for the phone (as it'll come straight from Google). This is because it takes additional time for manufacturers to add in their tweaks and UIs on top of the newer version of Android.
The second fastest to Vanilla stock would be a custom rom like CyanogenMod which takes the changes that Google pushes out into the Android source and incorporates them into the mod to get the latest version of Android on as many phones as possible.