I have one Block Erupter Blade, bought it about 3-4 weeks ago and I am currently at about 70% of ROI not including increased resale value. I managed to buy one for $240 before they shot up in price. I average about .008 BTC/day mining on Slush's pool. This will decrease over time as pool hashrate grows.

If you are willing to wait up to 12 months to make back your money, by all means, get started! Just keep in mind it will take some time to make back your investment, I would consider myself lucky for hitting ROI in 4-5 weeks. I would like to expand my mining but I am currently holding off to see if new hardware releases, etc. affect prices of current hardware before I invest more. Just be strategic with it!