The old Unix hacker in me likes Ksplice, from a hacker point of view.

However, I wouldn't use it, except in exceptional circumstances (e.g., there is a patch we have to apply now but we can't do scheduled down time). I want to reboot after an update--even an update that does not technically require it--because I want to know my system is in a state that can boot.

It is very annoying to do some update, not reboot, and then a couple of months later a power failure takes down your systems and when power is restored you get some kind of boot error and you are wondering what in the last several months you did that broke it.

A few minutes planned downtime now in much better than hours of unplanned downtime at some indeterminate future time.