You'll definitely see an improvement in speed. I upgraded to a 7200 RPM drive from a 5400 RPM one and it's definitely a worth while upgrade.
As far as battery life goes, I haven't really done any testing on this, but from a pure speculation standpoint with a 5400 RPM drive it would take longer for the drive to speed up and position the heads, and then read the data than a 7200 RPM drive would.
It depends on what you're doing with the laptop to determine it's effect on battery life. If I'm just browsing the web, doing forum posting and stuff, then then I get fine battery life, comparable to what I was getting with the 5400 RPM drive. If it's something like watching a video or continually accessing the drive then I get worse battery life. But when it's plugged in it's definitely a solid decision to upgrade.