It is. I was able to correct call drops from a hosted VoIP system by carving out a chunk of bandwidth for this. I was also able to correct inbound VPN connections to our main office constantly failing because our previous appliance ( Calyptix ) does not support traffic control features. It also drastically improved response over site-to-site VPN links and prevented some routing problems ( ospf packets not being given priority over bulk traffic, bfd packets being dropped ).
There is good documentation on this, but it's as much an art as a science and it requires you to understand your specific needs. I am by no means an expert, but this is engineer level work. Not to say that you can't do it - after all, I worked through it - just that you should be prepared to face a learning curve and a significant investment of time and effort.
Still, totally worth it. I don't know if you're a Safari Bookshelf person, but I think they have some good stuff in general on this. Somewhere there is a 'cheat sheet' that shows decimal, hex, and binary values for TOS, COS, and DSCP. If I can find it, I'll post here. You can find some good stuff on Cisco's site, and Cisco press has a book, End-To-End Qos, that's really good. I suppose it's a little dated, but I found it helpful.
Again, start here. The Linux Advanced Routing and Traffic Control project was where I was directed universally, wherever I asked. It's a pretty awesome primer.