Since the beginning of the year, one of the biggest shopping trends we’ve noticed has nothing to do with the latest clothing swinging from racks. Instead, it’s the onslaught of sites offering deals that flip or become active when enough people opt-in to buy at discounted prices.

You’ll find offers on everything from chiropractic services to wine tasting, but we’ve noticed a significant number worthy of a spot on any local style hound’s radar, including deals from local day spas, fitness studios and massage therapists.

Chances are, you’ve already heard of or tried more than one of the following:

Groupon

Joffer

Living Social

FreshGuide

Bloomspot

(Update: after publishing, we ran across yet another daily deal site: TownHog)

But once you realize there are no fewer than five of them offering San Francisco deals every day of the week (and we wouldn’t be surprised to find another one had launched since we began writing this post), it starts to become clear just how pervasive, not to mention successful at drawing in buyers, these social deal sites have become.

If things continue the way they’ve been going in ’10, paying full retail price for spa treatments, nail services, massages and fitness classes may soon seem out of the question. After all, how’s a girl to pay in full when she knows deep discounts on just what she’s after are likely to pop up at any moment on one of these sites?

We’ve already scored a $7 manicure, stalked a $40 massage and had our eye on 50 percent off gift certificates to local boutiques. And while we certainly enjoy saving on services at local businesses, we have to wonder whether five or more so very similar sites can peaceably coexist within just 49 square miles. We’ll be watching to see what happens (and paying less while we’re at it).

More San Francisco style news…