Our kids are 14 and almost 10, and we did not have a gaming system in our home (intentionally) until last December. I was very much against them. We knew so many people whose kids were "addicted" to them, and we also saw nieces and nephews being incredibly rude while playing with their portable Gameboys, etc., when other kids were around. Our kids were and are very much into reading, pretend play, playout outside, etc., and when they were little they would do computer games on occasion...most or all of the computer games had an educational component. Then the Wii came out, and it seemed different than other gaming systems. We planned to get it for them in December 2007, but it was a hot item, people were selling it on eBay for twice its cost, or more, and we could not find one anywhere at cost. Our kids had no idea we were considering it. Over the course of the following year, they played it occasionally at friends' homes, and I got positive reviews from many people that year. We bought it a year ago, and the kids were thrilled. They do not use it too often, mostly because they are busy with other things (thankfully), but they love it. (I've played it a handful of times and like it, too.)
I noticed that the basic price has gone down from $250 to $200, and that Toys R Us had a $99 special this week...unsure if it's still on or what the "catch" might be.... Also, while there is the cost for the system, there then are additional costs for the games, some accessories you may want, etc. My in-laws split the cost with us (which ended up being about $350 or $375) for the holidays. Also, at places like GameStop, you can get used Wii games for a little less than the cost. I know sometimes they have a buy 2 used games get 1 free deal, but they've never had the games I wanted when they've had those sales! You have about a week to try them out and return them when they're used, so it's not a bad deal!
I think the key with the Wii, as with television, computer games and general fun computer time, and other gaming systems, is moderation. We've always limited our family's time when they were younger re these things, and at this point it is a non-issue as the kids grew up without video games, etc., being a crutch or a babysitter and have other things they like to do.
Good luck! Have fun with it!