0. Tats are kind of my pet peeve. I know it's more of my issue than anything else, but they irritate me for some reason. May be the concept--I don't know--but even as a kid I would never write down reminders on my hands or draw on my skin.
I've see a few on guys and have thought it's a pretty cool looking design, but for the most part I just think people look better without them. I've never seen a woman and thought to myself for example, "That tattoo makes her look great!" Again, my own issue, and I know it. I don't think they're all trashy or anything, but I've definitely seen my fair share that give off that impression.
Then there's the issue of regret. Many people have their plan--pick out the right shop, the right artist, think long and hard about their design, etc.; and yet still there is regret in this population (not even including the population who gets a tat on a drunken night out). Tattoo removal rates are increasing (though to be fair so are tattoos in general); and those procedures are costly and not without their own complications. They're gaining more mainstream acceptance, but there is still stigma that can affect employment (obviously, picking a hidden location is a much brighter move).
As far as tattoo complications are concerned, they're not commonly talked about. I'd recommend doing a pubmed search and reading some of the literature before considering it as well. That kind of info isn't common publicized and definitely isn't broadcast in detail by your local tattoo parlor.