Hmmm, I've gotta say, there's sensible posts made by both sides... I suppose there's no one "real" definition of what a "tactical shotgun" is. I agree with Urbanly that, in practice, it should be designed to serve a specific purpose well, and that it should fulfill that purpose reliably. A shotgun is really more of a close combat weapon, and to me that says: compact, easy to aim, easy to shoot, with maximum damage caused. Personally, a semi-auto with a short barrel, Knoxx Spec Ops stock, and 6 round side-saddle would be perfect... No scope, no fancy paint, no shiny trinkets. In a close-combat situation, I don't want to have to cycle the action manually or worry about things breaking. If it jams, then I've got a 9mm semi-auto as a backup.
Then again, most of us won't be using these shotguns in a real "tactical" situation (unless zombies rise up...), so they don't need to be so reliable or take so much abuse. In that case, I think heat shields, flashlights, and red-dot sights look really cool, and I've got nothing against putting them on a shotgun.
In any event, as has been said before, modifying a shotgun should be personal: don't do something just because someone else says it's the way to go. If you like the way something looks, and it works for you, do it. I think JonnyBender has an awesome looking tacticool shotty... then again, the one novan3 posted has me drooling as well, and I think the combination of satiny smooth wood and bright metal looks better than most girls in lingerie.
There's a guy that works at the range I go to that has an AR15 all kitted out... the thing looks vicious. Laser sight, flashlight, scope, spare magazines, the whole nine yards. It looks really cool, and everyone has a great time shooting it. But, if the #### hit the fan, I'd still rather have my FEG handgun than his AR.