I think I registered my Shield with S&W, just like any other purchase that suggests warranty issues will be solved more expeditiously if you do so. Never ended up being necessary, but it sure helped with the wife's Walther.
Kimber is well known to address true warranty issues well beyond their stated warranty time.
If its a true warranty issue, most reputable companies will stand behind their product without the need to register it.
Yup-Kimber and Springfield Armory-Springfields sometimes comes with some nice freebies-like extra mags or shooters pack.
When I bought my EMP4 if you registered they sent out 4 free mags and some other swag.