I saw many people build their PCs with 2 or more monitors, and I like it. But the problem is buying 2 or more monitors needs to spend more money (about 300 bucks for one 22" monitor). It excess my pocket. At the end I decided instead of buying 2 monitors, I bought a 24" Dell UltraSharp monitor (only 378$ for a second hand one), and I have no regret. (And there is a good news, now the price is dropped to 358$)
A bigger monitor gives me more room to work. I don't need to move my head around like I would used many monitors. Also it helps to focus on my work, it's important thing. And in my spare time, I can enjoy full HD movies with my family.
Maybe someday I will buy another 24" monitor. But now I'm happy with my decision. It's worth to spend :-)
Some screenshots, they are big :-)