Hints and tips for high volume ELGG site - do you have experience?

I'm CTO for a company that is working toward putting up a new site using the ELGG software.

The current site is 10 years old and gets a LOT of unique visitors and a goodly number of return visitors each month (in excess of 1 million uniques) so we fully expect the new site to hit the ground running and climb in membership quickly.

I've done a basic architecture with a dual quad core Xeon (looks like 8 cores) 32 Gigs of RAM and 15k SCSI drives in a RAID 5 array as the initial machine. It will be running the MySQL database directly, and will be the DB server for what I expect will be a series of web front-end servers in the not too distant future.

In the mean time I have VMWare (free) server on the system and have configured 2 virtual web front-ends to make sure that I don't forget anything in the process of setting up multiple front-end boxen. For example, I realized that I have to NFS mount the uploads directory so that all the front-end machines can share it.

I'll initially be using simple round-robbin DNS for load sharing on the front-ends, and move to a load balancer when we get to more than 3 front end systems.

Is there anyone out there who is in the position of using separate front-end web hosts with back-end DB hosts at this time?

We'll be in beta release some time in the next couple of weeks and I'd really like to get some opinions on scaling things.

I've seen the notes about memcached and I'll likely turn that on.

I've also taken a quick look at the DBOptimisation module but have not implemented it yet as it says its for version 1.1

I'll also look at Oliver's Language optimization module

I don't expect we'll go live until the 1.5 version is out, even as beta. We'll be starting with a fairly minimal set of modules and add things as we go and learn.

Thanks for any comments you might have.