We purchased a Q1200 this year and really like it. We've had it loaded up with 10 large hamburgers and no problems.
The one thing I have noticed, though, it does cool off quickly with the lid open and can take a while to recover.
It is also sensitive to preheat time. Make sure you give it a good 10-15 mins to heat up to 400F or so before adding meat. Give it enough time to thoroughly heat up the cast iron grates, which helps greatly with keeping the temp steady.
For us the size is just right for the 3 of us plus a frequent guest or two and can be stretched to cook for a larger group.
Oh- this is a biggie- it seems to cook about the same on all locations of the grill if it is properly heated. If not properly heated or allowed to cool down too much and you rely on a high flame, the sections with fewer holes in the grates will obviously be slower.