I've just started doing some non-trivial stuff with Master Pages in Whidbey, and I'm already hitting some of their annoying limitations. Things that I've hit in just the last hour are:
- Nesting master pages disables the design view. That's right, as soon as you start nesting master pages, you're limited to the HTML code view (in both your master and content pages). That's such a major limitation that it's hard to believe MS even claims nested masters as a feature.
- ContentPlaceHolder controls render themselves as gigantic block elements in the designer, which can not be resized in any way. Essentially that limits their use to defining large regions on the page - forget about using content placeholders in small, precisely positioned regions in a title bar, for example (at least if you want any kind of decent designer experience).
Both of these problems have been reported already on Ladybug, with the predictable response - not going to be fixed. Grrrr..
UPDATE - Scott Guthrie comments that that ContentPlaceHolder's will fill their container, and so it's size can be controlled by placing it in a fixed-size container. Unfortunately, that's not the behavior I'm seeing with the Feb CTP - perhaps it's a bug. Also, if you want to design around the natural size of the content, the fill behavior is problematic.