Well, on the assumption that you're running an athlon 64 based system (big assumption, but I wanted to be safe rather than sorry), I'd like to remind everyone reading this who might be thinking along these lines, that except for one dfi motherboard that I know of, NO athlon64 system can run with all 4 memory slots full (socket939, not sure how this limitation affects socket 754 systems), and still run at 1T timings. It's a limitation of the memory controller vs the ... err.. I think it's the total capacitance of the circuit, iirc. Basically, when you start putting that many chips on the memory circuit without a buffer, something has to give.
So unless you can accept that limitation, which I believe will affect your overall speed by roughly 30%, depending on the application, avoid using more than 1 stick per channel.
I'm unaware of the limitations on intel based systems... and with socket754, the board does usually have 2 slots, which, attached to a single memory controller (there are two in a dual channel s939 chip, running in parallel), should result in the same slowdown, due again to the total capacitance of the circuit. Someone chime in here and correct me if I'm wrong.
Basically, athlon64, more than one dimm per memory channel is very very iffy, if you want to run at maximum speed.