I'm sure there are some geographies that for tourism reasons have specific seasonalities, but for the rest of us I'll suggest there is very little seasonality in this sport.
The only "downtime" I would see is from Thanksgiving thru the 1st of the year what with guys having family and other obligations and for some budgetary issues.
I say this having worked across a number of businesses where there really isn't much of a seasonality: people will talk about a "peak season" or conversely "down season" and it just is a way for a sales manager to try to pump the troops up or conversely is a "crutch" to explain underperforming.
The moral of the story: if you want to have a lousy Summer or want to work less it is easy enough to rationalize yourself that it is slow season.
Also consider that "buyers" in every business will blame the season on why they can't buy now or haven't been in touch lately. If one of your regulars doesn't see you all Summer then when he does and you (in a friendly way) ask him about it and he gives you "kids & vacations & whatever" take it for what it is: an excuse. Don't take a couple of very similar sounding excuses and translate it into a "slow summer season." Heck the rest of the year the excuse is, "I'm just really jammed up at the office."
Now a fair question might be, "In general, are things slower than they have been in the past?" Lot's of people have suggested this since the economy has gone south. But don't call it seasonality.