We are very near a decison on Zimbra NE for our school. We are a boarding school with 650 users, and will need to support 300+ concurrent users. Based on some reading here and elsewhere, I'm considering a server similar to this:
Dell 2950 III
single or dual quad core CPU
4 to 6 15K 146Gb SAS drives, configured as RAID 10
Ubuntu 8.04 64bit
For additional storage, we have an Equallogic PS5000 array with 14 SATA drives, 3x GB ports, and lots of free space. I am not certain how the performance of the SAN will compare with RAID 10 on the 2950, but our experience since migrating storage to it is that it easily keeps pace with or outperforms RAID 5 on the Dell 2950s we have. It is hard to compare user home drive storage with Zimbra storage though.
I would appreciate any feedback about the hardware, and especially from other similar sized installations. We will be migrating from Mercury/32, likely using imapcopy, with a mail store of ~50Gb.