Yep. While the Zalman is pretty good, I don't think it could cool a stock 4400+ passively. Which I'm doing now. And while the Ninja comes with a decent fan, you're not stuck with it (unlike the Zalman). You always have the option of easily switching out the fan.
Hi - I'm hoping to do the same with an X2 3800 soon. I'd be interested to hear what kinds of fans you're using to move air through the case. AFAIK these passive setups don't need a lot of air flow but they do rely on other fans to provide at least some.
I'm using a P180 case. I've replaced the 3 Antec Tri-cool fans with 120mm Yate Loons. I have the front intake and the one in the lower chamber (using lower HDD cage for drives) running at 840rpm. The exhaust I have plugged into the motherboard. With uGuru I set the fan to run at 8v (1020rpm) until 39C, at 40C I have it set to 12v (1350rpm). The top vent/fan hole on the case I have blocked. Here's a bad pic of my setup, I'll try to get some better ones. I'm also working on a duct for the exhaust fan.
I'm not sure if it's so much the weight as it is the design of heatsinks. The 7700 works because all the weight is right at the motherboard. Same with the Ninja, most of it's weight is at the base.
But look at a tower sink like Coolermaster's Hyper6, I've seen people on other forums cautioning about it being too top heavy. Coolermaster had a good design with that sink, but I think got a bit overzealous doing everything in copper. Scythe recently tried to redo a couple of their heatsinks in all copper, but for the increase in weight the performance wasn't that good. And the added weight wasn't welcomed either. So they were scrapped.
What I would personally like to see happen though in the ATX standard is cases accommodating heatsinks with a reinforced plate and standoffs. Intel has had this requirement for their server platforms for some time now. Definitely wouldn't have to worry about hsf weight when it's bolted to the motherboard tray.
I'm not sure if you already know of it, but if not be sure to check out SilentPC Review. A lot of ideas and knowledge about running powerful systems quietly or even silently. I used to think Antec fans were quiet, until I went there and found a whole other caliber of fan.