I'm pretty left-tendencied, but I'd be hard-pressed to feel bad about taking out the founder of Al-Qaeda. I'm happy he caught one in the face, though I'm surprised they buried him at sea. Makes me wonder when the conspiracy theorists will start spouting.
Is this really a left-right issue? 
I wouldn't try to frame as a left-right political issue, but yeah, if you don't believe in the death penalty, then I could see this being an issue for some people. Regardless of my kooky liberal leanings, I'm glad they did it and have tons of respect for everyone involved.
I guess I'm about as "left" like Schwarzenegger is a "republican." I'm for the death penalty, but feel it is used the most in states where it should be exercised with greater restraint, where defendants have been found guilty where there might have been a shadow of reasonable doubt.
OBL deserved to be incarcerated or jailed about the same way as Charles Manson; while he didn't directly kill anyone in those attacks, he's still responsible for inciting his followers to commit acts of terrorism, killing thousands of innocents. Personally, I'd rather see both Manson and OBL executed, as we've established their legal responsibility for the murders.