The U.S. Department of Justice spent the better part of a year and millions of dollars trying to prove that Oracle's ( ORCL) acquisition of PeopleSoft would end, or at least limit, competition in the business software market. The feds lost, of course, and if you'd care to know why the DOJ was wrong, look no further than the nasty dogfights that have developed since the beginning of the year.Two of the largest software companies in the world -- Microsoft ( MSFT) and Germany's SAP ( SAP) -- launched efforts to woo disgruntled customers from the embrace of the Redwood City, Calif.-based giant, with deep discounts, technical support and other goodies. Meanwhile, Siebel Systems ( SEBL) and privately held NetSuite turned the tables on upstart software maker Salesforce.com ( CRM), each with a campaign to attract customers by lowering prices. Efforts to poach customers from a newly merged company happen all the time, and often without much success. "We're very skeptical when applications vendors announce programs to lure away customers after an acquisition," said Jim Shepherd, an analyst with AMR Research. Indeed, Shepherd dismissed Microsoft's play for Oracle customers "as not worth the paper it's written on." But for Shepherd and other analysts, SAP's move is a departure from its own practice and that of the industry in general. Rather than simply proffering cheap license agreements, SAP took the unprecedented step of offering support for a competitor's product and even bought a small company, TomorrowNow, which had been providing support to PeopleSoft customers. And SAP was careful to target the initial offer at the 2,000 or so companies that already use both SAP and PeopleSoft applications. Why go to the mat now? Simply put, the software business is shrinking, and companies are fighting to hold on to their share. Oracle CEO Larry Ellison put in bluntly a few months ago: "This is the recovery -- enjoy it." And there are signs that the environment is getting worse.