Read this. (http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020424)
I think the technology in that article, while immature, sounds quite impressive, especially after speaking to Ross about the possibilities of cellular automata. I also like the ending of the article, stating that it would be possible to create any Turing-like algorithm using these biological elements. This makes me think they could go so far as to graft a biological computer into our brains so that we could compute faster.
Personally, I think the biggest and coolest supercomputer would be one involving human minds. I know that sounds like the Borg, but I just think it sounds pretty damn cool. However, failing that, it would be interesting to see if computers could be grafted to people's heads for specialized purposes, such as helping with mental retardation, etc.
There are obviously other things the article talks about, but I'll let you read about those.