I have two Shuttles at home and they each run 4 WoWs with no problem at all (though they only run one most of the time). They cost me about €1000 each over here in Germany.

The most recent is a quad core system with only 2Gb of RAM that my wife uses to two box on two screens:

1 Shuttle SG33G6 DeLuxe
1 Vista Home Premium (SP1) 32bit engl.
1 Corsair 2048MB CL4 DHX
1 MSI NX8800GT 512MB
1 Intel Q6600
1 500GB Samsung 16MB SATA2
1 DVD-RW Samsung SH-52030 DIE
With both instances running in "maximised window" mode with full graphical effects, she barely clocks up any CPU at all.

In other words, Shuttles are perfectly adequate boxing rigs. I have one dual-booting into Linux too, which may be worth considering if you're going for a dev course.

However... watch out for upgradeability. You can't run a Shuttle in SLI configuration, for example, because there's physically not enough space inside the case to take two monster cards. I suspect there would be PSU issues too.

I started buying Shuttles because I have limited space in my Frankfurt pad where I spend most of my time at the moment. If space isn't a huge concern, I'd probably favour a small tower system with a more respectable PSU and more space to plug things in!