Server hardware is incredibly inexpensive nowadays. For example, you can get a Dell 710R with an Intel Xeon 5690 6-core cpu, 32 gigabytes of RAM, a two-port Fibre-Channel host bus adapter, and dual gigabit Ethernet for less than $8000. Folks, that is a pretty stout box. And you can get even larger ones and much more memory.
What it comes down to is that you can probably afford as much memory and as many cpu cycles as you will ever need. Disk storage is not very expensive either.
The question is, how will this affect how you design your applications?
I used to think that it was necessary to build "stateless" applications so you could have enough scalability and minimize the number of of AppServer agents you have to run.
Now I wonder whether it is worth it. It is definitely less work to build stateful applications and dedicate an agent to each client. With such powerful servers as the one I described above, it may even turn out to be practical.