All true, but we are running a 100K (Canadian) blade center, and at 255 apaches per server and 10 blades, thats ~2500 concurrent users. You have to have a pretty honking Sun box to manage that, certainly within the same price range, and another 15K buys me 40% more power.
One white-box machine (say 2Ghz) with 2 gigs of ram, running the Worker or Event MPM can easily handle ~2500 concurrent clients.
Buy more machines for redundancy.
-Paul
