There's a good roundup of some of current biofuels from algae technology on world changing .com.
I guess the key is to develop an algae that will grow fast enough and in great enough density to make extraction from the growing medium efficient. I think that one of the processes mentioned, (Green fuel's )may need the algae to be conditioned to increasing levels of carbon dioxide. I'd be interested in hearing whether this is a problem or not, and if it is what they're planning to do about it.