The AT7 features a slot layout of 3 PCI, 1 AGP and 4 DIMM. The reason why Abit decided to only include 3 PCI slots on the board was because all of the extra onboard controllers make it impossible to fit any extra PCI slots on without going out of spec. The 4 DIMM slots are a great addition, considering we are used to seeing only 3 on most boards. The lack of CNR/AMR/ISA slots show that this board is directed solely towards the enthusiast, rather than the OEM market.
There is a decent amount of room around the CPU socket for any large heatsink/fan units you may own. As with most Abit motherboards, a thermal sensor is located on the inside of the socket to measures temperatures from the bottom of your CPU. While the most accurate way would be to have the sensor touching the core itself, this method is sufficient, just don't think of the readings as being totally accurate. You should also note that there are four mounting holes around the CPU socket for those of you that own heatsink/fan units which don't use the convention retention mechanism.
One qualm I had about the layout of the board was the placement of the CPU socket. Due to the fact that it is located towards the top of the motherboard, people with smaller cases will find it very difficult to install/uninstall their heatsink/fan unit without removing the whole motherboard or motherboard tray.
The ATX power connector is well placed so that your power cables do not run over the top of the heatsink/fan unit, restricting airflow. The IDE and Floppy connectors were also logically placed so that they are not in the way of the PCI slots and can be easily reached.
One unusual thing I noticed about the AT7 was that the CMOS battery is seated vertically, rather than the horizontal positioning we are used to. The reason for this is that, with all the onboard components, Abit had to think of every way possible to save space on the board. Another thing to note is that the AT7 also uses a 3-phase power solution in order to reduce heat produced by the MOSFETs, capacitors and regulators.