I go year round but typically notch it up a bit in the fall. Apart from being my favourite season, summer and to a less extent spring is a bit difficult with football season going full swing with games and practices taking up three nights a week usually. So when football ends in late July or early August, I have more time in the evenings for cooking outside.
To be honest, I don't understand why there's such a powerful psychological deadline surrounding Labour Day with barbecues getting put away and cottages being closed up etc. People are missing out on some of the best time to enjoy those things since it's still nice out during the fall and peak bug season's over, and you won't get sunburnt nearly as easily as during the summer. September and October are both excellent months to be outside. I remember when I bought my fire pit last September at an end of season sale at Cabela's, the lady helping me out mentioned that fire pit season was pretty much over and I pointed out that it had really just begun, now that it was starting to be cool in the evenings. She gave it some thought and then agreed it was strange to consider the start of the cool weather the end of the season for heat generating fire pits.