It's just a big loop. I mine as a hobby to chat with people and feel like I'm taking part in a big stock market game! Then I take the profit from that (a small amount) and use it to pay the electricity bill caused by the mining :< In the end, it's all fun

As a serious investment, I think the fact that knowing you'll get your miner in a determined amount of time is much more valuable to you. Sure, a market analysis of the two now will show the BFL as a better deal for hash rate, but by the time you get your miner, things may have changed significantly. Also, the erupters just look so darn cute