As I investigate the Wood Elves more and more I find myself falling in love with these arboreal nasties.
Their cost notwithstanding, they seem very very solid in the late fourth and fifth edition rules set. Eat a charge with the Willow Aspect, then switch to Birch (if you're gonna strike first) or Oak (if you're gonna strike second) for the next round and clean up. Unless you're fighting something with an absolute ton of attacks, they seem golden.
What concerns me is that they end up in little lines of five or so and they're not THAT tough, so how do you get the most out of them in an actual battlefield context?