Well I too own a Seeeduino board and the spacing option was one of the features that sold me even though I haven't yet installed extra headers.
I've stayed away from Uno purchase so far mostly because there was bound to be early bugs and compatibility problems (which there were some bootloader issues early I believe and the quick version ide20 vs ide21) and the fact that there weren't any USB host examples out there to take advantage of the new USB hosting capabilities.
Which by the way brings up another great opportunity for some vendor/person to offer the Arduino community. That would be a simple shield that just has the new 8U2 chip, usb connector and support components such that when usb hosting applications show up one could utilize them with older Arduino boards. Sound useful?
Lefty