If you have experience with previous versions of XAML, you need to know about some key differences in Windows 8 XAML from previous versions. There are missing elements, some of which simply don't have an analog in Windows 8, and others which have a functional replacement.
Some of your old friends from those platforms are not present in Windows 8. Some were left out because they are not easy to fit into a touch-optimized experience. Because this is a version 1.0 product, some desirable features didn't make it into the released product simply because of lack of time.
The differences are too extensive to present a comprehensive list, but here are the panels and controls you are most likely to miss:
Except for WrapPanel, these missing elements have no replacement element that supplies near-equivalent functionality. The user interaction patterns for TreeView, DataGrid, and TabControl are not easy to translate to a touch-first mode, so analogs were not attempted in the first version of Windows 8 XAML. DockPanel and UniformGrid are lesser used panels, and that's probably why they didn't make the cut.
Expander, DatePicker, and MonthCalendar are missing as well. With Expander, it is an open question of whether it fits the Windows 8 UI conventions. However, it's clear that line-of-business apps need date controls, so you'll probably see those ...