This is of course a very personal opinion, but a year into fairly consistent networking, I have a few thoughts I'd like to share. 

(1) Networking is a great way to build a referral based business, but it can be all consuming. Watch out for signs of tiring out without seeing some return. Networking is a long haul project and to let others feel comfortable with you and your business can't be forced or tied to your own personal timeline.

(2) Allow yourself one purely social group.... without expecting any type of business down the road. It makes networking fun... and if it's not fun, you're going to dread it.

(3) You want something from networking over time. Try to quantify your expectations. If you are looking for customers, try to figure out if you're seeing progress toward building a customer base. If you're trying to build a second tier network, are you seeing others refer you. The truth is somewhere in between, but do keep track to some degree as you practice patience.

(4) Don't forget about other sales and marketing efforts. I don't think that networking works all by itself in the short term. Fill in the early days with other business generating activities as well. 3-4 years down the road, you may be the go to person in your industry, but that won't happen immediately.

I am a member of Network in Austin, SWING Austin, the Dripping Springs Breakfast Club, BNI's all about Business Chapter and the Hispanic Chamber of Commerce. I'm a fan of all forms of networking, from the loose design (show up and shoot the breeze) to the more structured forms like BNI. Give yourself a chance to find your style and rhythm over time.