Mobile plans?

Most Windows users aren't even aware that are alternatives and just because they use it, I wouldn't assume they are happy with it. I would suggest you ask users if they are actually happy to get the answer.

While the ability to move panels might make it more flexible, that flexibility comes at a price. For instance, the first deployment of GNOME 2 I did, a lot of users removed panels or window switcher and called up support because they couldn't figure out what happened. This was solved by making it more harder to do it by default in subsequent versions but I was amazed at how much trouble it did cause in the first place. When we wrote internal help documentation, if someone else moved the panel around, other users get confused because what they see in the help doesn't match reality. Now with GNOME 3, I can be reasonably sure what the UI would look like and if I were still doing some desktop administration, that is a big advantage.

Now GNOME 3 could still offer the flexibility if they had the ability to lockdown the UI for large deployments but this requires a lot of careful planning and development and isn't as simple a choice as you make it out to be.