I don't know about you, but trim takes forever to get done in our house. This is mostly because we spend so much time thinking about how much time it's going to take that it takes a lot of motivation to work on it... then we're always surprised with how fast it goes up... then when we take a break we start all over again with the no motivation... it's an evil cycle. That being said, we have now completed the trim on the bottom of our beams in the kitchen and have even primed the beams!
Our beams are made out of just regular plywood but in the end we don't want them to look cheap. We used corner trim on all corners of the beams and flat trim on the seams (and where there wasn't seams but where it would be symmetric) as well as boxes around the lights. It looks so much better now and the trim hasn't even been caulked (another no motivation task)!