Looking for installations with a large number of concurrent users

Hello all,

We're implementing a fairly large J2EE application, I'm estimating around
450,000 concurrent users at high peak. Performing reads and writes and
we have a very high performance requirement.

I'll be using connection pooling (probably the pooling delivered with
Geronimo).

I'd like to get an idea of "how big can I go". without running into context
switch storms, or hiting some other wall.

The design actually calls for multiple databases but I'm trying to get a
good idea of the max size / database. (I.e., don't want 50+ database servers
if i can avoid it)

We'll be on 8.4 (or 8.5) by the time we go live and SLES linux (for now).
I don't have hardware yet, basically, we'll purchase enough hardware to
handle whatever we need...

Is anyone willing to share their max connections and maybe some rough
hardware sizing (cpu/mem?).

Thanks

Dave