Given Powell's involvement with the Irak war and given Obama's opinions and plans about Irak; I would dare to say that this endorsement (if it's even remotely connected with Irak) speaks volumes.
Didn't Powell disagree with Bush about the invasion of Iraq? Is that why he stepped down?
Secondly, I fear that his endorsement means nothing. It would be like Hillary Clinton endorsing Obama. I don't see the connection other than he was a liberal republican and should have ran for president himself, he would win in a landslide.
A very interesting article about the Rules of engagement in Somalia, he noted that it would take brut force to win over the nation of a very proud people, as his rules were in place in Somalia, news spread fast that whomever brandished a weapon would be shot, and considered a hostile target, and most importantly all 'technicals' were considered hostile.
Things changed when a sniper engaged a 'technical' and told the AP that a pregnant woman got shot. Effers at the media portrayed US as a bunch of warmongers who would engage any man woman and child to defend themselves.
Things changed after that, Powell stepped down, I do believe (please check spelling I already know i'm going to hack this) Schwarzkopf stepped down.
( I think i'm going to check reference on this and report next)
Edit: no Schwarzkopf stepped down after the Gulf War, amid failing health reasons.