Does anyone use guest posting for back links?

Yes

First, visit Guest blogging: Looking for guest bloggers or guest post? Join MyBlogGuest! and www.bloggerlinkup.com and start a thread telling people the niche you write on and share any sample work of yours that you have. After you have a few solid guest posts you will have more success seeking out bloggers with more popular blogs to guest post for. Do a google search for your keyword or a shorter broader keyword in your niche, and then make it a Blog search by clicking "Blogs" on the left-hand side. Find some popular blogs that look like they sometimes take guest posts and email them *from a name@website.com email NOT a gmail or free account. Share with them links to a few of your previous posts and any other credentials you've acquired.
I don't know, a zillion times? Guest post backlinks are great and actually are the best backlinks to get in my opinion. Let me break it down...

Guest post backlinks have the potential to be relevant, dofollow, contextual, high PR links. What more could you want? Oh yeah, they send traffic too!

You might not be posting on really popular blogs right away, but do a few to get there - each post will certainly help and still give good backlinks while you build your profile.

Because it's hard to write a great post about Best Cheap TV Reviews

Guest posting is an amazing tool for bloggers but most blogs accepting guest posts will have strict guidelines around the quality of writing, topics etc.

Don't think of this as just being a means to getting a backlink because chances are you won't be allowed to link directly to any of your own work as it creates the perception the post itself is just self-promotional. You will however, get a link in your bio.

What guest posts are great for is building your reputation and credibility in the blogosphere. When another blog allows you the opportunity, they are basically saying "we trust you to write for us" and that's a great thing. It increases your social capital.

You will more than likely increase your readership and your subscribers, but you have to have compelling content to keep them.

I agree with barrywheeler. Quality of content is very important for doing guest posting. To find sites for guest posting relevant to your niche, use this search string in google - Your keyword "write for us". You can filter good, high PR sites and mail them requesting guest post submission. Some allow you for contexual link, which has more value, while some allow you to include your site link in author bio section..

Guest posts can improve your blog as long as strict quality control is observed. You will also have more time in promoting your blog. It's like hitting 2 birds in one stone.

Because guest bloggers are allowed to express their ideas, you will have different point of views and perspectives which then makes the blog active. You will also gain good relationship with other bloggers.

Lots of good here; the two sites mentioned by BenJackson are great for finding blogs to post on, and bloggers to write posts for your own site, and build relationships. As Barry said, it is vital that the posts you provide are great quality and relevant to the blogger's niche, and your own. This really helps build your "webutation."
Here are a few more search strings you can use: your keywords "submit post". your keywords "submit article" to find bloggers who are open to guest posting.

Thank you.

Absolutely! That's a strategy that I've employed to achieve top rankings for a variety of websites.

The best part is that if you execute guest blogging properly you can achieve sales/regular visitors as well. Which is even better than only trying to achieve rankings.

Guest blogging can even make you an "expert" in your niche in very little time! Just remember to provide excellent value and continue to regularly comment and be an active member of the community.