I have been testing Moodle 2.0 for some time now and there are a number of issues which are pending in the current display of columns, blocks, etc.
I have made the following observations using the default Standard theme.

1- In Site Administration mode, all 3 columns are correctly displayed

2- Inside a course, on the course home page, the right column is narrower than it is in Site admin mode. To see this, put a calendar block in both pages.
2a. When using the format white theme, left and right columns are even narrower. Using Custom Corners theme, they are ridiculously narrow.

3- On a course home page, in Edit mode, Add resource and Add an activity lines are misaligned on the right. This bug was reported many months ago but has remained unfixed so far, I wonder why. See MDL-14138 and MDL-14140.

4- If a teacher places all the blocks on the right, leaving the left column totally empty, an "empty left column" is still displayed. Expected behavior (as per previous versions) would be to make the center column (Topics) spread to the left.

Looking forward to a fix,
Joseph