I have owned some very light and comfortable aluminum frames along the way.
Carbon is sweeet no doubt.....but aluminum is a bigger bang for the buck. If you can afford an all carbon frame then that's great. If you only have 1k to 1.5k in your budget then you can get more bike if you choose aluminum. Many(perhaps all) of the pros in the peloton will be riding carbon. They don't have budgetary issues though. They are always going to ride the newest and best thing on the market. That's how the manufacturers get us to buy them. We don't necessarily have to try and keep up with what jan Ullrich is riding. Don't forget....the motor is the most important thing.