I know last year I had plants spread a lot further than I expected and I had them at least 18 inches apart, sometimes even more. I am far from an expert but I would say a little further. They look very spaced at first but those thing will grom like crazy. He are some picks from mine last year. Like you, tomatoes in the back.

I had mine at 24" centers and it was not enough room for most of them. I will have mine at least 30" centers this year.

Dale

Sorry, here are the pics. As you can see, some of them just blew up.

June 8th

August 9th

Wow! Turned into an impassable jungle. That's really great :)
I have a very small garden. Perhaps half the size of ripperbt. The regular vegetables will get all that space. My peppers have always been grown in containers, so I never really have had to consider it. 30 inches definitely does not seem to be overkill when they grow like that!

I have a question though. Let's say that you have 1 row 10 feet long (120 inches). You can fit 4 plants at 30 inches, or 6 plants at 20 inches. (assuming just a pure division, where the outer plants are located 30/2=15 inches from the edge in the 30 inch case vs 20/2=10 inches for the 20 inch one). Which configuration will yield more peppers? I am really wondering, because it seems like there would be a sweet spot (yield only! not considering the ease of finding and picking!). It seems like it would be highly dependent on the plant and the size requirements. A lot of seed packets have recommended spacing (most peppers would probably be in the 2-3 feet range). I would venture to guess that those numbers really should be pretty optimal for that particular species (given good and nutritious soil and happy plants).

It wasn't too bad getting to the peppers but this year I have to do something about my lawn:)