I started bitcoin mining with my Raspberry Pi and an ASIC miner, just for fun because I like to tinker. I doubt that I'll get rich off this, but I just wanted to try out this "real" digital currency.
I'm not 100% sold on it yet, it does have some great advantages (i.e. decentralized, low transaction fees), and some disadvantages (i.e. governments might not like it), so it remains to be seen if it will be viable.
In the meantime, I'm mining 24/7 with a goal to get to 1 BTC by the time I'm 90.