Why weren't you out at the amusement park this summer? That's what Cedar Fair (NYSE:FUN) investors should be asking anyone within earshot after the regional park operator posted a disappointing interim report Thursday night.

On a same-park basis this year, total revenue at Cedar Fair is coming in 2% higher through Labor Day. That is the result of a 5% gain in per-capita spending, partly offset by a 3% decline in attendance. Things were even worse in the telltale month of August, with turnstile clicks off by 5% and total revenue coming in 1% lower than it did a year earlier.

As a result of recent lackluster trends, Cedar Fair anticipates coming in at the lower end of its full-year expectations of $950 million to $980 million in revenue and $320 million to $340 million in adjusted EBITDA.

There are several reasons why this shouldn't come as much of a surprise. The company may have bitten off more than it could chew when it acquired the Paramount Parks chain from CBS (NYSE:CBS) last year. It didn't add enough marquee attractions to its flagship parks this season. There are also several factors like pesky oil prices, weather, and economic sentiment that are clearly beyond the company's control.

It's not just Cedar Fair, though. Companies that typically thrive during the summer have been struggling. Last month, Great Wolf Resorts (NASDAQ:WOLF) talked down its guidance after posting a wider quarterly loss.

It has been a hot season at the multiplex, right? Wrong. Regal (NYSE:RGC), AMC, and Carmike Cinemas (NASDAQ:CKEC) all posted stagnant results or slight top-line dips in the second quarter. Even if there were a few celluloid hits that came out after the end of the quarter ended in June, three of the four highest-grossing flicks of 2007 came out in May.

Jamba Juice is at its best when warm weather brings in the thirsty for the chain's signature smoothies, right? Wrong. Parent company Jamba (NASDAQ:JMBA) posted a 3.5% drop in comps during its latest quarter.

Music promoter Live Nation (NYSE:LYV) posted second-quarter gains, but did so despite what it calls a "weaker concert season" compared with 2006.

So while investors need to make Cedar Fair accountable for its performance, they also can't fault the operator for the murkier trends surrounding many of the summer's leisure plays. Still, that's the rub with seasonal plays. Now that the shine is gone, the summer of 2008 seems so far away.

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Longtime Fool contributor Rick Munarriz enjoys taking his family on coaster treks over the summer. Yes, he's been on all of the Cedar Point coasters, except for Maverick. He owns units in Cedar Fair. He is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.