Ah, yes. This is one that many new writers lose sleep over. MFAs can cost a lot of money and time. But do they really teach you anything? It depends on who you ask.
Here's my opinion: It really doesn't matter if you get an MFA or not. There are other factors that influence your success as a writer much more. Many very successful writers have MFAs. Many do not. It's a matter of figuring out what is personally right for you.
I am very happy to have my MFA, and I had a good experience getting it. I went to a low-residency program (becoming more and more popular now, these programs allow you to keep your job and your life and only be on campus limited times during the year) at Warren Wilson College. I went to the program because I wanted to make sure I had deadlines that forced me to write. I also met some wonderful fellow-writers who have been wonderfully supportive, and made some good contacts with successful fiction writers. Some people complain of heirarchy and cliques in MFA programs (i.e. who gets to sit at Tobias Wolff's table?) but there was little if any of that at Warren Wilson.
Some people talk about a particular kind of literary writing, what one friend of mine called the "fly-fishing-with-my-alcoholic-father story," being the only kind encouraged at MFA programs. I did not find that at Warren Wilson but have heard that complaint leveled at other programs. You might want to see what writers came out of various programs to see what you think.
Now then, would it make you stand out to an agent or editor to say in your query letter that you graduated from Iowa? Well, yes, it probably would. But if they don't think there is a market for your work, they won't take it on, no matter where you went, and if they do think there is a market for it, they will, no matter whether you have an MFA or not, or where you got it. There are many other things - publication in literary reviews, acquaintances with name authors who might blurb your work, to say nothing of the actual quality of your work, that will also make you stand out to a potential agent or editor. And there are ways to get these things without getting an MFA - networking, goint to readings, writer's groups, writer's conferences, to name just a few.
So, the bottom line is, what do you want? If you want deadlines, continual feedback, and a community of writers, and you have the time and money, you may want to investigate MFA programs and see if one is right for you. (Extension programs at universities, like UCLA and Berkeley, can offer similar advantages and be lighter on the wallet and time commitment.) If you have the discipline thing down and prefer to work in a more solitary way, maybe it's not for you. But I can honestly say that in my experience whether or not you have an MFA really makes very little difference to agents and editors. So you should do what feels right to you.