Until the official announcement today, we had heard precious little about Mr. Donilon. Obama announced that his current National Security Advisor, Jim Jones, was stepping down and that Tom Donilon, the current Deputy National Security Advisor would be taking his place.
According to Who Runs Gov, Donilon is a long time Democrat political figure. From 1999 to 2005 he worked as a lobbyist solely for Fannie Mae, but he’s been involved with politics for much longer:
He has also served in policy roles, working as assistant secretary of state for public affairs and as former Clinton secretary of State Warren Christopher’s chief of staff. In that role, Donilon was intimately involved in many major foreign policy issues, including negotiating the Bosnian peace agreement and the expansion of NATO. 
While his appointment seems common-sense considering his present job as Deputy NSA, it doesn’t come without contention.
In veteran U.S. journalist Bob Woodward’s new book “Obama’s Wars,” which gives an inside look at how Obama crafted his Afghan war strategy, Donilon is shown as deeply skeptical of a big troop increase in Afghanistan.
Donilon was part of a circle of close aides who urged Obama to push back against the military’s request for a large U.S. troop increase. 
It turns out that his stint lobbying for Fannie Mae, one of the root causes of the current financial mess, was also not without issue:
In 1999, Donilon accepted an executive vice president position at Fannie Mae. 
..Thomas Donilon, oversaw an aggressive, backdoor lobbying campaign by mortgage giant Fannie Mae to undermine the credibility of a probe into the firm’s accounting irregularities, according to a 2006 government report on the company.
The effort — which reportedly included attacks on the funding for the oversight agency, the Office of Federal Housing Enterprise Oversight, and an attempt to launch a separate investigation into OFHEO itself — was ultimately unsuccessful, and regulators eventually discovered top Fannie Mae executives had been manipulating the company’s financial reporting to maximize their bonuses.
According to politico.com he was a VP during the time period that the investigation covered
Donilon left the firm as it was mired in an accounting scandal in 2005, three years before Fannie Mae’s spectacular collapse when the mortgage market imploded in 2008. Investigators never accused Donilon of wrongdoing in the accounting scandal, but Fannie ultimately paid $400 million to the federal government to settle charges that the company misstated its earnings between 1998 and 2004. The government sued three top Fannie Mae executives to recover millions in bonuses based on the allegedly falsified reports, but Donilon was not among them.
A former official who led one of the main investigations into Fannie Mae said Friday that Donilon didn’t play a role in the misstatements but tried to pressure lawmakers to derail the probe.
And ABC news had this to say about the whole thing:
Facing accusations of misstating its earnings from 1998 to 2004, Fannie Mae settled with the Securities and Exchange Commission for $400 million in 2006, although it did not admit any wrongdoing.
How about his views on national security issues? Well, it turns out, he’s a yes man. He lines up perfectly with Obama’s stances on everything. Although unnecessary, this should do much to boost Obama’s confidence in his disastrous handling of foreign affairs.
Donilon views a nuclear Iran and North Korea as the gravest national security threat facing the country. He has called on the president to pursue robust diplomacy along with stricter sanctions on these two states.
Unfortunately according to Woodward’s “Obama’s Wars”, he has the same lack of foreign affairs and military experience as Obama as the outgoing Security Advisor pointed out in this exchange.
First, he had never gone to Afghanistan or Iraq, or really left the office for a serious field trip. As a result, he said, you have no direct understanding of these places. “You have no credibility with the military.” You should go overseas. The White House, Situation Room, interagency byplay, as important as they are, are not everything.Second, Jones continued, you frequently pop off with absolute declarations about places you’ve never been, leaders you’ve never met, or colleagues you work with. Gates had mentioned this to Jones, saying that Donilon’s sound-offs and strong spur-of-the-moment opinions, especially about one general, had offended him so much at an Oval Office meeting that he nearly walked out.
Donilon is not the typical academician with which the the President usually surrounds himself and the new Security Advisor will be one less dissenting voice in the administration. Just one less sanity check for a President that desperately needs every last one he can get.
 Thomas Donilon – http://www.whorunsgov.com/Profiles/Thomas_Donilon
 New Obama Security Advisor Clashed With Military – http://news.yahoo.com/s/nm/20101008/pl_nm/us_obama_jones_6
 Obama Transition Member Oversaw Fannie’s Lobbying – http://abcnews.go.com/Blotter/Politics/Story?id=6269682&page=1
 Tom Donilon’s résumé: Policy, law and Fannie Maehttp://www.politico.com/news/stories/1010/43348.html#ixzz11qGlm5Pl