All our installs have been all 64 bit mostly using 16 GB of memory, with some using 8. The ease and sturdiness of replication has been a significant benefit for redundancy as well as splitting applications up between read and write. I hear in 6.0 they'll be leveraging replication to provide a synchronous mirror type env. One of the nice features of SQL Servers replication model is the fact that the transactions are stored in the distribution database, and I've been looking at a way to leverage the MSrepl_commands table so that we can replicate out to mysql.