Specifying a new pink, I wondered for a moment whether I should specify 8Gb of RAM. Then I realised that "main" computer I've ever owned hit the RAM limit. The Sinclair QL was effectively limited when you had to solder a second planar over the motherboard to take the RAM and that has a megabyte. The 386 maxed at 24Mb, I think, even though it had 32 in it. The 486 took 64, then stopped. The pentium I had took 128Mb, but the cache subsystem pooed itself when you went over 64Mb, so I stuck at 64Mb. I skipped P2s, and ended up with a lot of P3 servers in i8xx motherboards, which are limited at 512Mb, and they've all got 512Mb in them. My P-M is limited at 2G, and it's got 2G in it. My last office desktop was specced at 8Gb, but it pooed itself at 4Gb, so we sent it back and got a dual opteron which we successfully put 8Gb in a Tyan motherboard which allegedly takes 24Gb. So that last dual opteron is the only machine I've ever had which I didn't max the RAM on, but I believe that machine's still going, unless the company busted it since I quit, so it may get upgraded yet.
Anyway, we come back to the specification for a new pink, since the old one has had everything replaced at least once (yes, including the PSU, CPU, motherboard and network cards, and I did it very fast and you didn't notice) and many things twice, and I've run out of spares.
So if Rackable Systems have anything that supports 24Gb of RAM, I think we'll take it. Perhaps this is also the point to migrate to Xen.