I dont feel that the 2.5 hours spent on OMM per week is wasted at all. We have anatomy second semester at UMDNJ and I can tell you from having taken OMM for a full semester before touching anatomy that OMM really does help you understand anatomy more easily. It provides extra instruction and reinforcement on nerve innervations, bone articulations, body mechanics, physical diagnosis, and just the awesome power of human touch. Some of this stuff we breeze over in Physiology, Anatomy, Neuroscience and other classes and some of it is barely mentioned so this is just a bonus. Sure, I admit that I am probably never going to professionally use OMM but that does not mean I regret learning it! I can also say that the 2.5 hours it takes to go to this class is not going to detract from my other studies because either way, my studies get done and I still have plenty of time left over to watch Scrubs, work out, read, post on SDN, and play video games. I do feel lucky to be here though because our OMM docs are really open-minded and cut through the crap but anywhere you go one of the most important skills you will learn as a medical student and even as a doctor is to cut through the crap and dissect out the relevant and useful information in any subject!
As for your other question about what OMM is, well there is plenty of reading for you to do about it but I can tell you there is research backing a lot of it up. Check out the journal club sub-forum of the Osteopathic forum and do a search in pubmed. It most definitely is not the cure-all end-all of medicine, at least in my opinion, but in the very least it is a powerful diagnostic tool and handy to have in your bag of tools in addition to medicine and surgery.