Visual Studio 2008 had one great feature - guidelines. While this may seem as irrelevant feature to casual observer, it is indispensable if you are used to editing text document in RFC style. It was useful even in code files as a signal that line is getting too long and you need to consider continuing your code in next line.
Visual Studio 2010 (beta 1) gave us brave new editor with lots of features but, as you may guess it, without this one. For all people who loved this feature, it is quite sad that it will be omitted from final version also. While I can understand that it was never official feature to start with, I cannot get over it.
However, life goes on. There is great extensibility support in new Visual Studio so someone may even write this. Who knows, if time allows, maybe even I will do that.
[2010-04-06: Paul Harrington did it. Guidelines are back.]