not very, my teams at least have a lot of turnover throughout the season. You don't want to have too many of your players on the same one however. But don't avoid someone who is a good value because of a bye week.
Bye week 9 has a lot of studs... So careful there as you could end up with four or five starters on the same bye week... I've seen it already. I'm a big time believer in SOS. Which is why I've moved Brees ahead of Manning in my rankings. Guys that have really easy SOS tend to have Great fantasy seasons. I researched this last year going back to 2010 and I know for a fact SOS is a factor.
I don't look at bye weeks. Like SNP says, there is a fairly decent amount of turnover per team. And if I have the chance to land a stud receiver on a week 9 bye and have another on a week 9 bye, i'm not going to let it change my mind.
I've never put a ton of stock in bye week planning. But to echo @Kurt, I always study SOS and playoff schedule, and I too note a lot of good players on week 9 byes. Generally, I do my player rankings independent of SOS and playoff schedule, but then use those factors to tweak rankings and as tiebreakers when I like more than one player.
i don't think they are real important unless one of your best players is injured and it is obviously effecting your team.
