Personally, I have diversified my investments in start-ups, mining shares, and mining hardware.  I did some math this morning and discovered that my mining shares are almost exactly on par with my hardware investments (Original purchase ~2.25BTC w/ equivalent daily ROI).  However, I find that the two erupters I purchased have been the most intellectually fulfilling.  I wanted to get into mining, but the pre-order scams are daunting and single CPU/GPU mining is not profitable.  It was certainly fun to learn more about mining and the purchase of the hardware provided the impetus for me to do so.