I have two 24" widescreen monitors. I like to work with large full-height windows directly in front of my eyes, with smaller windows off to the sides. This calls for a symmetrical grid, where the right and left monitor grids are mirrors of each other.
I never split my main windows horizontally, only vertically. But my side windows (maybe call them "portlets") might be half height.
I sometimes split my screens 50/50 left-to-right, and other times 65/35.
With all of those constraints, I came up with a grid layout that provides what I want with 16 zones. I haven't decided if I want to add zones for minimize and maximize. The current implementation doesn't have them.
The grid works a lot like the dual-screen grid that is currently included with the base installation, except that it mirror-images the left and right monitors, and allows for a 50/50 split in addition to the 35/65 split. (Maybe the dual-screen layout is a 30/70 split. I can't tell exactly.)
The attached grid allows for layouts like
50/50 split full height
|--------|--------| |--------|--------|
| | | | | |
| | | | | |
| | | | | |
|--------|--------| |--------|--------|
65/35 split full height
|-----|-----------| |-----------|-----|
| | | | | |
| | | | | |
| | | | | |
|-----|-----------| |-----------|-----|
50/50 split with portlets
|--------|--------| |--------|--------|
| | | | | |
|--------| | | |--------|
| | | | | |
|--------|--------| |--------|--------|
65/35 split with portlets
|-----|-----------| |-----------|-----|
| | | | | |
|-----| | | |-----|
| | | | | |
|-----|-----------| |-----------|-----|
Or any combination of those. Of course, there's nothing keeping you from using 50/50 on one monitor and 65/35 on the other, or full height portlets on one and half-height portlets on the other.
[Edit Jan 10 2008: Improved trigger zones]