I have been picking at the edges of merged cells for a while now. We support horizontal alignment 'merge across selection' and fully support horizontal spanning.
Merged cells are a slightly tougher nut to crack because they also merge vertically.
I have have some notes on how to handle that in an efficent way and will probably add this before the end of the year. We have the specs for the quatro pro file format. However, that has not been much time to play with them. If anyone is interested, it would be an interesting project. The following comments are owned by whoever posted them.