The concept of a secret agent hiding his identity from his significant other worked will in True Lies (and probably even better in the original French movie that it was actually a sloppy remake of), and it worked well in Mr. and Mrs. Smith. I don't know how well it would work for a whole series... episode after episode of false alarms where it looks like the significant other will find out, but doesn't!
Kor
Well Jamie Lee Curtis does find out the truth in the movie so in theory the next step would be having the family keeping the secret from the world,maybe their parents or choldren and also you might have them working a fake job as cover so you got co-workers who don't know what is going on. Actually when I think about it, I kind of think of "Dexter" only if Dexter was a secret agent instead of serial killer.
Jason