i just stumbled on bitcoins (and mining them) last week and have been running through the many positives specific to me. if done right i see this being a very nice hobby/part time job.
i already have several pc's that i keep running 24x7 and have already got them mining at about 1GH/s. in their current location they help me heat my basement office that would otherwise be using electic baseboard heaters (it isn't connected to the house HVAC).
i will likely take some spare/old hardware and build up 2 dedicated miners, stick them in a basement utility room while routing hot air from that room into my HVAC for 9 months/year and vent outside the other 3.
if all goes well and see some returns but too much wasted electricity (expecially in the summer where i am dumping heat) i have a storage/auto workshop that i rent with free electricity although no internet. it is part of a larger warehouse/industrial shop so as long as i don't go crazy the juice for a rig or 2 won't be noticed.
other indirect benefits are the awareness this has put on me of efficiency and attention to detail. i may no rake in massive profits directly from mining but i think when i look at the big picture i will be better for the experience if i play it smart.
thanks to all that have contributed to the effort and i have learned from - i'm sure there is much more to go as well.