I tried installing an extra 256M in my 256M laptop (a Thinkpad T21).  
It crashed repeatedly when I tried compilations.  I got the following 
(hand-typed) traceback once:

uvm_fault(0xe343f5e4, 0x0, 0, 1) -> e
kernel: page fault trap, code=0
Stopped in pid 2967 (cpp0) at uiomove+0x63: movl  0x34(%edx),%eax

My guess is that it's either the SODIMM or the socket, but I'm not 100% 
certain -- I think I've seen other posters mention uvm_fault problems 
with 1.6.  And this is a stock 1.6 installation.

		--Steve Bellovin, http://www.research.att.com/~smb (me)
		http://www.wilyhacker.com ("Firewalls" book)