Interesting article regarding the scalability of Exchange 2000 and 2003 in terms of memory and CPU.
The maximum amount of memory that Exchange can make use of is 4 GB (old news) but more interestingly is that the article recommends disabling the use of PAE (Physical Address Extension) on Enterprise and Datacenter versions of Windows with the use of the /nopae boot.ini switch (If using the /3GB switch) - as it puts unnecessary strains on the system.
New facts to me are the notes regarding the scalability of Exchange in terms of CPU's - on a 8 CPU system Exchange supposedly can fully utilize 900 MHz CPU's but it isn't able to utilize e.g. 8 1400 MHz Xeon CPU's (Unless you are running e.g. anti-virus products on the same boxes).