I modded mine to hold an extra rack by drilling holes roughly midway between the existing water pan level and the top grate. I used like 2" long 1/4-20 bolts as the brackets nutted on the inside to secure them. I someday plan to add a coulple of more racks for mass production of ABTs. Right now the one extra rack is great for turkey legs but sees its share of other stuff too. I also added a cheap dial thermometer to the lid, not really critical to cooking anything, but fun to know if I am up to temps yet. A small hole or two in the sides for thermometer probe wires has been disscussed in other threads before and I think this is a good idea. It could help keep from pinching a wire with the lid. A metal side wing or shelf to stick magnetic backed thermometers to is also something that I haven't gotten around to yet, so I say that it is in the planning stage right now.
I have been kicking the idea of a thermostat or rheostat around also, but I fear that low temps will not produce the smoke and lead to having to make a smoke pistol of some sort.
All in all the unit is pretty good for what it is straight out of the box (Some assembly required) About my only real gripe is having to unstack the top grate for access to the lower level food and this only gets worse when adding extra grates. A little planning and forethought and this isn't really that much of an issue, but if you are going to mop alot you need to think about this.