Siebel Systems (NASDAQ:SEBL) has seen better days. The dominant provider of software for managing customer relationships reported yesterday afternoon that it would fall far short of second-quarter revenue estimates. Shares dropped nearly 13% in pre-market trading.

In a statement, Siebel said it expects revenue to come in at $301 million, roughly 15% lower than the Street's estimate of $353 million. The company blamed the shortfall on "unexpected delays in purchasing decisions by certain prospects and customers." Translation: We couldn't close the deals we needed to close, sorry.

Without a crystal ball it's impossible to know why these critical deals -- worth at least $50 million combined -- couldn't get done. One answer could be competition. Siebel has some of the toughest competitors in the business in Salesforce.com (NYSE:CRM), Oracle (NASDAQ:ORCL), and PeopleSoft (NASDAQ:PSFT). The changing economics of software could also be playing a role, as fellow Fool Tom Taulli recently pointed out.

Regardless of the reasons, investors don't appear to like where Siebel is headed. They've made their opinion known by repeatedly clicking the sell button, sending Siebel's shares lower by more than 30% this year. Can you blame them? It's not like yesterday's news is the lone ding on a pristine record for Siebel. It was only last week that the SEC filed a civil action against the company for violating Regulation Fair Disclosure for the second time in two years.

The good news, if there really is any, is that Siebel isn't alone. PeopleSoft warned that it would miss earnings estimates, too. (Although the firm predictably blamed the bad news on Oracle's hostile bid.) Other apparent victims of a declining appetite for software include Veritas (NASDAQ:VRTS) and JDA (NASDAQ:JDAS), both of which issued earnings warnings. (Veritas got the worst of it, getting hammered by more than 35% yesterday.)

Perhaps the investing lesson here is that it's not enough to dominate a good market with a good product. Good management is equally important. Sadly, that's the one thing that seems to be in short supply at Siebel.

Need more Siebel coverage? Try these on for size:

  • Siebel spilled the beans, again.
  • Fool Rick Munarriz raised a toast to founder Tom Siebel upon his resigning the CEO post.
  • Although the results were overhyped, Siebel made progress in the first quarter.

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Fool contributor Tim Beyers thinks that the SEC should slap the handcuffs on executives that ignore Regulation FD. Yep, that means you, bucko. Tim owns no shares in any of the companies mentioned, and you can view his Fool profile here.