How long is "a few seconds" for Kill Skills?
The Kill Skills in Borderlands 2, like BL1, all say they last "a few seconds" and don't give explicit lengths. Since they're not listed in the stats for the skill (as length for Kill Skills doesn't increase) there's no way to tell from the interface alone.
Exactly how long do these skills last? Do they all last the same length across classes?
Solution 1:
In Borderlands 1, kill skills lasted 7 seconds.
I've just tested it with my Axton's [3/5] Quick Charge, and it is 7 too.
There is a guy who got 10 seconds from a pre-release video. Assuming he is not simply mistaken, either it was some earlier version, or Salvador's skills are different, or skill level affects its duration.
I'll go level up and time my Quick Charge again, meanwhile anyone who is able to time other abilities is welcome :)
Solution 2:
Corroborating Orc JMR's answer:
I didn't think that there'd be a difference between the characters, but I tested them anyway. I time them with my iPhone, using the same systematic uncertainty of my reaction time. Start: when I see the icons pop-up. Stop: when I see the icons disappear.
Siren: 7, 6.7 seconds.
Brick: 6.8, 6.7 seconds.
Mordecai: 6.8 seconds.
Roland: 6.8, 6.5 seconds.
Pro-tip: On-kill skills (OKS) have a hexagonal outline.