Smoothie chain Jamba (Nasdaq: JMBA) is facing plenty of blender-armed challengers these days. Between McDonald's (NYSE: MCD) recent rollout of McCafe smoothies and Starbucks (Nasdaq: SBUX) with its Vivanno line, it's not hard to find a refreshing fruit smoothie when you need one.

However, can Jamba's biggest competition be itself?

Jamba posted lackluster quarterly results yesterday. Revenue fell 16%, and last year's profit turned into a net loss -- a big issue since this is Jamba's seasonally strongest quarter.

It's not as bad as it looks. Revenue was supposed to take it on the chin. The company's in the process of closing a few stores and transferring some of its company-owned stores to franchisees. In fact, revenue of $66.1 million was ahead of the $65.7 million that analysts were expecting.

The net loss is also a bit deceptive. Back out charges related to the closing of seven stores and its refranchising efforts, and Jamba would have been squarely in the black. It still would have earned slightly less than the $0.04 a share it rang up a year ago, but at least it didn't totally blow its primetime quarter.

What's problematic for me -- not just as an analyst but as an investor -- is that comps still fell by 2.7% at its company-owned locations during the quarter. It may not seem like much of a dip, but keep in mind that comps fell by 5.3% during the same quarter a year earlier and 10.3% during 2008's third quarter.

In other words, comps have slipped by more than 17% in three years. Jamba has beefed up its offerings along the way to include everything from oatmeal to breakfast smoothies to a beefed up line of baked goods -- and its popularity continues to wane, year after year.

There are some positive developments. Yesterday it announced a franchising agreement to enter Canada, following the company's move to begin franchising in South Korea.

Its relationship with food giant Nestle (OTC: NSRGY.OB) continues to expand, with a line of fruit-based energy drinks debuting next year. No one is going to give Jamba much of a chance against Red Bull, Hansen Natural's (Nasdaq: HANS) Monster, and Coca-Cola's (NYSE: KO) Full Throttle, but even a thin slice of the market can have a dramatic impact on the smallish Jamba.

Jamba's guidance for 2011 is encouraging. It sees a return to positive comps, the development of 50-70 new locations, and impressive operating margins of 18% to 20%.

Unfortunately, we have a right to be jaded. A year ago, Jamba was also telling investors that it was expecting positive comps in 2010. It's not going to happen. Jamba's guidance can be as nutty as its granola-topped smoothie meals.

I'll hold my shares for now. The presence of the world's largest fast-food chain handing over McCafe smoothies through its drive-thru windows doesn't appear to be obliterating Jamba's model -- though it's also not educating the market in a way that I had initially hoped.

Jamba can be special, it just needs to sprinkle in some of its signature boosts into its income statements.

Have you tried the new McCafe smoothies? What did you think? Share your critique in the comment box below.

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Longtime Fool contributor Rick Munarriz is about a 10 minute walk to a Jamba Juice, making that trek often. He does own shares in Jamba. 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, and it comes with a free immunity boost.