I recently brewed two test beers (comparing bitterness with and without a hop bag).  The resulting beers were nothing spectacular, so I decided to try another experiment.  I've always enjoyed a good pepper beer so I decided to give it a try.  After researching a few recipes on the internet, I decided to "dry hop" one beer with 8 oz of jalapenos and 1 oz of serranos and the other beer with 4 oz of jalapenos and 3 oz of serranos (all weights after cutting up peppers and removing seeds).  I filled hop bags with the chopped up peppers and threw them in my kegs (beers had already finished fermentation).  The next day I threw them in my fridge and tried a sample, just to get an idea of how they were doing.  Already, the first beer had a massive jalapeno aroma with a spiciness that left a tingling on the lips and tip of the tongue.  The other beer did not end up with as much aroma but left a slight burn in the throat after swallowing (not too much flavor impact).  Given how much impact they had already caused, I took the bags out after one day.

I've been told that the flavor mellows over time, but they were already as strong as I would ever want them.  If you try this on your own sometime, I would not recommend using any more peppers than I did.  If you used a smaller amount, you may be able to leave them in for a while longer.  I do recommend testing the development of the beer frequently.  Of the two, I like the tingling in the front of the mouth and the aroma contributed by the first beer with more jalapenos.