Stupidity is contagious. It gets us all from time to time. Even respectable companies can catch it. As I do every week, let's take a look at five dumb financial events this week that may make your head spin.

1. Stop the press
What's black and blue and red all over?

Shares of CafePress (Nasdaq: PRSS) fell sharply on Tuesday after reporting disappointing quarterly results.

The one-off printing specialist held up reasonably well during the second quarter, but its guidance calling for a sharp sequential decline in revenue and profitability during the current quarter took the market by surprise.

We're in an election year. CafePress' more than 3 million virtual shops should be buzzing with partisan propaganda given the way that many people in this country are voicing their political agendas. How can sales not be rocking the vote?

It could be the high prices that consumers have to pay for the company's wares. Folks may be politically charged at the moment, but their pocketbooks aren't stupid.

2. Sharing a car means sharing the pain
Zipcar (Nasdaq: ZIP) isn't the speedster the market thought it would be.

The leading car-sharing service is shifting into reverse after posting a problematic quarterly report.

Revenue fell short of even Zipcar's own guidance, and a small deficit isn't sitting well with analysts banking on breakeven results. However, the scarier part of this story comes from the company's guidance.

Zipcar sees a surprising quarterly deficit at the midpoint of its outlook on meager sequential revenue growth for the current quarter.

Car sharing is a trend that's here to stay, and Zipcar now has more than 731,000 members. However, when membership grows by 21%, yet revenue climbs a mere 15%, there's a Zipster utilization factor that needs to be addressed.

3. Just desserts
OpenTable (Nasdaq: OPEN) took a hit a month ago when Barclays Capital analyst Mark May suggested that the company was peaking.

May's channel checks showed that the leading online dining reservations specialist was about to post a sequential dip in revenue for the quarter ending in June. It would be the first time that's happened at OpenTable.

Well, after cranking out revenue of $39.4 million during this year's first quarter, OpenTable's year-over-year revenue climbed 15% to $39.6 million in last night's second-quarter report. May was close, but no after-dinner cigar.

Now, the midpoint of OpenTable's guidance for the current quarter suggests that sequential growth will be a challenge this time around. However, OpenTable's guidance of adjusted profitability this year to clock in between $1.54 a share and $1.66 a share exposes May's target of $1.47 a share as too low.

4. Knight and day
A trading glitch is something that a financial services giant can overcome, but that may not be true for Knight Capital Group (NYSE: KCG).

Shares of Knight Capital shed nearly two thirds of its value yesterday after revealing a software glitch that cost it a $440 million trading loss.

Knight may be a big market maker in retail U.S. equity shares, but it may not be big enough to absorb the hit. More importantly, its credibility is going to take a hit even if it is able to avoid bankruptcy or seal the deal on a quick acquisition.

5. Biotech goes bio-blech
Dendreon (Nasdaq: DNDN) took a hit after posting disappointing quarterly results and cost-cutting initiatives.

The cancer drug developer may have posted a narrowing deficit in its latest quarter, but the cash burn continues. Dendreon is closing down a manufacturing facility and laying off 600 workers. The move should save the company $150 million in annual costs, but trying to preserve capital paints a gloomier picture about its pipeline's prospects.

Dendreon's CEO is calling this a "new course for Dendreon," but the market didn't like it.

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