for me, it's worth it for a couple reasons. i know exactly what i'm smoking and what has gone into it. and the main reason i started growing was that i was always getting overcharged, and even if i'm not the most efficient grower, it's still cheaper (per weight) for me to grow my own. and as i get older it gets harder for me to keep those "connections" to good stuff and good deals. so i just make my own.

and another added bonus, for me, is that i find the gardening kinda therapeutic. it can be frustrating at times, but it's usually peaceful and relaxing for me, watching the plants grow, reaping the rewards, enjoying my own work. so i factor that in as well.
i guess i look at it like, for what i spend on electricity, supplies, etc, am i getting at least that amount in return, if i had to pay full retail price? most of the time, i'm getting a sweet deal!
i do have to remind myself of that sometimes, when it's time to pay the utilities bill. but when i look at how much i pay and how much i harvest. it's still working out in my favor.
for example, a standard 1/8 (of kind) around here runs about 40-60, so an oz would be around 400 at that rate. i don't spend that much each month, and overall i get way more for my money.
btw, right now i run one 400w hps, a 150w hps, and a 200w cfl
i guess there could be a point at which it becomes more cost than it's worth, but the satisfaction of growing my own is very appealing to me. it would have to cost me more (in time and money) than i could buy it for, for me to stop.
just my 2 cents!