Linking Strategies in LinkedIn

How do you use LinkedIn? Who do you connect to? Do you use LinkedIn Groups? This post on the NextWeb triggered me to answer these questions publicly.

Resume
LinkedIn is an interesting platform. I've been using it for several years now. At first I basically uploaded my resume to LinkedIn. I hardly visited LinkedIn after that, except for excepting link requests.
Some time after that LinkedIn introduced Answers. I followed several topics there, but stopped after about a year. The quality of the questions was horrible and it seemed I didn't get anything back from the answers I gave.

Groups
I also joined several LinkedIn Groups. Groups is interesting and it keeps me coming back to the LinkedIn site. Right now I'm following 27 groups, mostly in my area of expertise (intranet, social media, knowledge management, enterprise 2.0, social business). Most of the groups have interesting discussions. The update in my email every day helps me keep up with what's going on in there. If I see an interesting question that I can answer, I'll jump in. And, regularly, I also tap into the knowledge of the group members. The quality of the interaction and the people's knowledge in the groups is usually great.

Linking
Of course, I get invites to connect in LinkedIn. Regularly people that I don't know personally, contact me via LinkedIn with a request to connect. (This is also encouraged by a LinkedIn Group setting allowing group members to link directly to each other. I usually uncheck this setting.) I accept invitations to connect when I know the person quite well. I've talked with him/her, preferably face-to-face. I want to be able to say something about that person, if somebody asks me about him/her. For instance, when a recruiter is looking for someone in my network and asks me about him/her, I want to be able to give a recommendation. If I can't do this, I won't connect with that person. Of course I hope I'll be able to do so in the near future. Sometimes this interaction via LinkedIn even leads to a live meeting with that person.

What's your linking strategy?
I know there are different linking strategies. What's yours? Do you link to everybody who sends you requests? If so, why? Do you also join groups? How do you follow what's happening in those groups?