I've recently upgraded to Visual Studio 2012 and haven't have any problems except for the fact that comments beginning with "//todo" no longer show up in the task list. I have absolutely no idea on where to start looking for a solution to this problem as all of the keywords are too general.
I came across other similar questions where the answer was that the file wasn't open containing the //todo comment, but that is not the case for me. My todo comments do not show up even when the file is open in front of me.
Actually there is a dropdown control at the top of the "Task List" window and if you use the Visual Studio 2012 Dark Theme the dropdown looks like a label. If you click the "User Tasks" text, you will see "Comments" selection which lists your comments that contain "//todo".