If these reports are true there are still major security problems about boarding planes, especially in terms of international travel

I think it's fair to say that governments need to cooperate with each other more in order to catch people using stolen passports.  Even if these two passports used by god knows who and for what purpose had nothing to do with this plane's mysterious disappearance this type of thing should not be going on at all.  

There is an article in the Wall Street Journal online that mentions some very disturbing findings.

1.) The investigation into the fate of the plane has been complicated further by revelations that two passengers appeared to have boarded the plane with stolen passports, prompting airline executives and aviation officials to say that foul play can't be ruled out.

2.) Military radar readings indicate the plane may have reversed course, the country's air force chief said. Gen. Rodzali Duad said the military is still studying the radar data, and added that it is corroborated by some civilian radar data.

3.) A European security official said it wasn't uncommon for passengers to board flights using stolen passports. In addition, Beijing has emerged as a bustling transit hub in recent years, providing connecting flights to Europe and elsewhere from other parts of Asia, buoyed in part by a 72-hour visa-on-arrival program.

4.) On Sunday afternoon, a statement issued in the name of a previously unknown group claimed that the disappearance of the plane was a political act aimed at the Chinese and Malaysian governments and referred to last week's attack in a Chinese train station by alleged Uighur separatists. It stopped short of a claim of responsibility. Malaysian officials said that they were unaware of any claim of responsibility but would investigate all possibilities.

The Associated Press add this:

5.) PARIS (AP) — Interpol said Sunday that no country checked the police agency's database that held information about two stolen passports used to board an ill-fated Malaysia Airlines flight.

"Whilst it is too soon to speculate about any connection between these stolen passports and the missing plane, it is clearly of great concern that any passenger was able to board an international flight using a stolen passport listed in Interpol's databases," Interpol Secretary General Ronald K. Noble said in a statement.

Even though the Interpol has been sounding the alarm about passport fraud for years, people have managed to board flights a billion times without having their passports checked against its stolen-documents records, Interpol said.

6.) Reuters says there were possibly more than two people travelling with stolen passports.