Thanks man, like Jogro said above they may not be the most efficient way to grow but they have other qualities that make them very desirable for small time growers. If you do it right you can easily grow a gram a day per plant.
Agreeing that you should be able to get that yield, grams/day-plant probably isn't the best way to compare different kinds of grows, since so much if that depends on plant size. A better way to go is grams per square foot of grow area per month which takes plant size into account.
I'm actually starting to think that based on really short flower times/high turnover, minimal need for training, and the ability to run lights 24 hours in flowering, growing lots of small autos in a small "sea of green" may actually be THE most efficient way to grow, at least in terms of yield per square foot per unit time. That is, *IF* you're willing/able to put up with relatively high plant counts. Lots of people aren't because of legal plant count limits.
As one extreme example, the "Secrets of the West Coast Masters" book describes growers pulling 1-2lbs per three month grow cycle from regular photoperiod plants under one 400W HPS. These are guys with a lot of experience, growing highly trained "monster" plants in huge pots, and with everything (lights, temp, nutes) perfectly optimized after experience with multiple grow cycles. So that's about 10 grams/day per plant. Sounds pretty impressive, right?
Imagine under the same 400 watt lighting over a 4x4' space, you were to grow 16 autoflowers in a mini "sea of green", each in its own 1 sq-foot area. The autos go from seed to bud in 8 weeks, and each yields 1 ounce. So now you're yielding 1 lb (16 ounces) every two months, or 1.5 lbs every three months. You'd have to cull out males to get your 16 females, but in what otherwise amounts to a pretty easy regimen from seeds, you're already doing as well in absolute yield as the so-called West Coast masters! If you can get 1.25 ounces/plant in square foot plants, (which is probably possible), now you're at just shy of 2lbs/3 months.
I think getting 1 gram/day out of plants that small is probably going to be tough, but if you could do that, your 16 plants would yield 1.4 kg in 90 days, or just over 3 lbs!
In any case, because you would need to run 24 hours of lighting to get those yields from the autoflowers, you're not going to be quite as efficient in terms of ENERGY usage as the West Coast guys (who are getting their yields with 12-12 lighting). But in terms of yield/space or yield/month, you'd probably be doing at least as well, if not better.
Now, if you can devote a small space to planting seeds, and growing them up to 3 weeks of age before they are sexed, the males discarded, and the females transplanted into final 1 ft pots, then you'd only be putting sexed three-week old seedlings into the flowering area. Now the "flowering" part of the grow cycle is only 5 weeks, meaning you could harvest your 16 ounces every 5 weeks. Per 12 weeks, that's 38 ounces, or nearly 2.5 lbs per three months, with only one ounce per plant.
Realistically, if you're a small home grower, growing only for yourself, you probably don't need pounds. You also probably don't need a full 4x4 grow area. If you were to go to a tiny 2x2' space with a 250 watt light equivalent, you could scale down the sea of green to only 4 plants (plus maybe seedlings). If you grow from seed every time, that's 4 ounces/8 weeks or 2 ounces a month. If you go with the seedling/flowering combo, its 4 oz/5 weeks or 3.2 ounces/month.
Bottom line is, the fast flower time and small size of the autoflowers *COULD* be used to get great yields in a small space, if that's what you're after.
The limiting factors are going to be plant count, and quality of the autos.
