I don't regulate, either (though, my kids are younger, I'm responding thinking about my 9 yo since I consider her a pre-teen). She doesn't happen to care about the wii or her DSi at this point, but she does enjoy using the computer to look things up, play games, watch music videos/shows, etc. She also has a cell phone she texts a little bit on, and talks to a couple close friends and her cousins. She has an ipod for music, and a MP3 player that displays short videos. She doesn't use the last two devices daily, but I wouldn't limit them if she did.
Anyhow, I guess my thing is that her electronic use doesn't tend to get in the way of other activities. She doesn't have homework to worry about (then I could maybe see encouraging finishing it before using the computer - but that's a bridge we'll cross when we get to it - I'm not a fan of homework, TBH), and she happily prefers to be outside riding her bikes or playing basketball with her little brothers. I'm just playing it by ear, for now. If I felt like essentially allowing unlimited use was detrimental at some point, I'd likely step in and place some gentle limits, I think. I don't know that I would go as far as some of DS's friends who only allow video games on the weekends, but I might bug DD more to get off the computer and do something else - if I were worried.
FWIW, my 7 yo (so I know, not a pre-teen or teen) goes through periods when he plays the wii a whole lot. Like not too long ago when he got Mario Galaxy 2 and it seemed like he played it for 4 days straight (except he didn't really, b/c he had school and ate and of course slept
) but he was determined to beat the game - and he did, on the 4th day. Anyhow, my point is that since then, he's used the wii very rarely - in fact, I don't think I've seen him on it for several days now. Even at a younger age, I don't put a limit on gaming for him, and he's shown me that he can regulate it himself. He's active, super thin (almost too much so), and like his sister would pick going to the park or riding his bike over sitting on the couch, any day.
ETA: this approach is just what works for us, right now.