how long veggin

Can anyone tell me how long a plant should veg for before switching to a flowering light cycle? Thanks in advance

It depends how big you want it to get. The first time you grow a strain, assume it will triple in height from start of flowering to finish, and make the switch at about a third of what you want the final height of the plant to be.
If you're growing indoors with lights above the plants, it's not really worth growing taller than about 3 feet, as the lights won't penetrate much further than this and you will only get light, airy buds around the bottom of the plant. With sidelighting it's not such a problem, and you can grow to as high as you have room for.

The answer I always see basically comes down to "you can flower anytime you want to"
Generally I think a month of veg is recommended regardless as a min though.

You can flower from seed, or from rooted clone, as do quite a few SOG growers.
It allows for quicker turnaround time and (arguably) greater efficiency since you're only providing it light and nutes that contribute to bud growth, rather than weeks of 18+ hours per day lighting and veg nutes.
The whole idea with SOG is to have lots of small plants that get replaced as soon as they are harvested, so the room is always full. Flowering from the word go fits in well with this ethos.

I pretty much follow Hairy Bob's advice but I try to start them into flower when they get about half the size the flower room and light max height can handle which just about coincides with when they start bumping into the lights in the grow room which happens to about half as tall as the flowering area. Still usually have to tie down a few of the tall ones but dont think I have broke the 3 foot rule of thumb yet. Seed genetics is unknown but nearly got to think it Indica or mostly so since it tends to stay so short. I have some real seeds from Merry olde England cooling their heels in the dresser drawer, AK 48 from Attitude, but have to clear out the current grow afore I got space to fool with em. Might even hang onto them till the fall and the weather cools off. I'm well over a hundred in the grow and veg room both as we speak. Would be ashamed to treat good seeds in such a shabby fashion. Might should have waited to order them I suppose.

Thanx peoples. I hear that if you let it veg too long, the buds won't be as good. Is there any truth to this other than the light issue?

I'm not sure...not experienced enough!

I usually let them go about 2 months, generally though it depends on the size of your space - I've heard 6 weeks is about the earliest you can flower...some guys on here have experimented 12/12 lights from day 1 though

If the plant grows too big for the room or for the light/s, then quality will suffer, but it's not to do with the veg time.
A friend of mine who's been growing nearly ten years flowers his mothers after they've been growing a year or so, (they start taking up more space than they're worth after you've cut them back so many times) and imo it's at least as good as anything else he grows.