can nintendo sue people for talking about mods and hacks on public sites (eg. this site) or encouraging it??
When will people learn mods and hacks aren't illegal. Homebrew is not illegal. Pirating their games
is illegal.
So to answer your question, Nintendo can't take any legal actions if you mod/hack your system, (including talking about it).
Playing homebrew games is legal so you can do that all you want also. However pirating copyrighted material like real Nintendo games puts you at risk and it is possible for Nintendo to sue you, but unless you're making a lot of money selling pirated games they wont waste their time on you.
Talking about it is legal under the free speech law, but if your not doing anything illegal (like piraing) than you should be fine.