From a small business perspective:
The problem with twitter is that whatever you tweet gets buried in the sand. The only thing that makes it through all this junk is retweetable content. But not every high quality content post makes it retweetable just like a good youtube video doesn’t go viral just because its good. Very good content usually gets buried. What i found twitter to be good for is if large media companies refuse to cover an event and you want to follow whats going on. You just type it in the search and find all the online activists who are posting about this topic. I have found that twitter is a complete waste of time if you work result oriented. Its next to impossible to get followers which are really interested in your topic.
I own yomodel.com with a twitter following of 3290. The Yomodel facebook has almost 20,000 likes. About 1000 Twitter followers i got over time through my site, about 1000 followers i got through www.twiends.com (by paying for them) and about 1000 followers i got through a competition i run. The impact was really minimal. The idea behind using twiends was that maybe if i get enough followers there will be a tipping point. But now i highly doubt that because a lot of people on twitter follow so many people that i believe not even 1% read your post. Facebook on the other hand has an algorithm that decides whether your content makes it to the main feed of your subscriber. The only drawback is that the threshold to get to the front page gets more and more difficult as people subscribe to hundreds of pages. Still, Facebook has send ten thousands of visitors and i know of other webmasters and businesses that have had success with it. Unfortunately though, the likes that somebody does on your post are not prominently shown to their other friends. So it doesn’t go viral. I am not going to make recommendations here for twitter or facebook because its a waste of time as they are not going to read it. So facebook acts more as a kind of mailing list rather than a viral marketing tool. You have to push people to your page and then you can mail them things from time to time. If you want to have success with Facebook, you need to create an application that when users interact with your website their activity gets posted on their main feed. This is the best way to go viral. Unfortunately, this is more prominent then if they interact with your facebook page.
My experience with google is that is increasingly hard to get to the top even if you make your page more interesting. I am no newbie to SEO and optimizing your website to get to the top of google but i don’t make artificial links. Thats just not my style. I keep on improving the site as a strategy. What i found is that unless you are targeting 3 word phrases or more in google you have no chance to get to the top. I have had huge movements in some keywords like “model agencies” once on the second page and then again vanishing from the top 100 for that keyword. This just made me extremely frustrated with google when i see hundreds of useless pages being above mine.
I am just hoping that one day websites will get rewarded for the quality and interest by their members rather then by strange algorithms. I don’t think thats an unrealistic wish. I just think we are not there yet but we will get there.
If i had give points to the usefulness of these services to small businesses and how much time you should spend on them i would say
Facebook Wins with 7 out of 10 points, Next Google with 4/10 and 1 for twitter
Spend your time on facebook. Figuring out how to make people link to your website