I've told quite a few people, mostly when they're over and say "what games do you have?" and I respond by plopping a spindle of DVD-Rs on their lap.
I've only installed it personally on one console - my own.
When people ask, I usually tell them the basic process - in the Wii Zelda game, there's a horse that can be named, and with a special save file, the horse's name is much longer than the Wii expects, causing it to crash, and then the save file lets me boot anything I want, and from there I can install things like this that lets me play burned games.
A lot of people ask me to do it for them, but decide against it when I tell them of the bricking risk, or I decide against it for them because they don't fully appreciate the risks involved, or will hold me responsible even if I tell them ahead of time.
Only one other person I know has hacked their Wii as a result of what I did to mine, but he did most of it on his own. The only thing I did was help him set the booktype on his burner to DVD-ROM for his DVD+Rs, give him Starfall, and help him install Starfall after he told me B+2 didn't work....
Personally, I've found that the best method is to simply over-exaggerate the risk of bricking. Most will decide against it, and some will go online to learn that the bricking only occurs if you screw up. At that point, they'll see how easy it is to do, and do it themselves. For the few remaining, just tell them that you don't want to risk breaking their Wii, and that if they really want to do it they should find out themselves.
If someone actually goes through the process of learning how to do it and doing it themselves, they should be able to figure out how to get apps and other things themselves too.
