One of the biggest friction points for me right now is setting up layouts. There are a number of flaws/bugs with the current implementation of guides that make it incredibly difficult/frustrating to set up a layout and begin working on an actual design. Since that is usually step 1, I've found myself quitting the application and jumping back to Adobe before I even get a chance to test out the majority of the software. The two biggest issues for me are:
Guides do not display x/y coordinates anywhere while being drawn. If guide is released and then moved, coordinates are displayed in a red tooltip. This means in order to accurately place my guides I need to draw them once, then move them.
Guides do not snap to whole pixels. I'm constantly struggling to get my guide aligned with a whole pixel, but keep getting stuck above or below my target by a few tenths of a pixel (i.e. 149.8, 150.1, instead of 150px).
In addition, the ability to automate some guide/layout functions would be invaluable. In particular, setting up columns and gutters for the 960 grid (http://960.gs). There are also core iOS/Android layouts that could be included too (actionbars, sidebars, etc).