Multisite and Clustering

Hello,

I’m currently running a PoC on WordPress as tool to build a Blog Farm for every company employees’blog.

We’ve set a WP (freshly updated to 3.0.1), and turned the multisite on.
The database is clustered, it’s totally hidden and we have no issues with that.

BUT … we have two Apache servers (for loadbalancing) and we’re currently experiencing some issues when submitting a file, for instance, a picture because each cluster has his own filesystem.

What’s supposed to be done to get WP(MU enabled) to work with server clustering ?

We gonna also need some simple way to submit Themes and Plugins, and be able to make easy version upgrades.

What is recommended ?
NFS ? and if yes, what do you recommend to use as root ? (wp root directory, wp-content ?)

Thanks for further wise answers ??