First, you should understand what MLS is. It was not designed as a marketing venue for homes; rather, it's a simple way for brokers to negotiate compensation with each other, so that Real Estate Agent A can tell Real Estate Agent B, "Sell my listing and I will pay you X." Period.
My local MLS, which was named #1 in the country, is still way behind the times. It allows me to upload approximately eight tiny (two-by-two-inch) pictures and about three sentences of description. I'm not even allowed to link to anything. How is that a viable marketing tool?
Look at Zillow, Trulia, and Yahoo! Real Estate and you'll see how much the MLS has been eclipsed. It's become just an outdated method for real estate agents to protect their turf. Some systems aren't even Mac compatible.
If you're selling your home yourself, don't worry about a Multiple Listing Service. You can put your home up for viewing on hundreds of websites, and you can add up to thirty-six large, high-definition photos in your listing. You can have paragraphs of description about your home. You can attach listing brochures and other files, which interested buyers can view online or download. You can add background music or a voice-over about your property's features.
In short, MLS is a tool. Not even a great tool. You can do so much better on your own.