Alternative Biochemistry

"Follow the water" is a common mantra when searching for evidence of extraterrestrial life. After all, you can support life without water, right? But is that necessarily true? Obviously we have a bias towards carbon based life forms since that's what we know, but what about silicon-based? Or an ammonia solvent? The wikipedia entry on the subject of alternative biochemistry is quite expansive on the subject explaining, for example, why silicon wouldn't work. Of course, many of the arguments are still based on certain assumptions built upon how we know life on earth operates, but it's still an interesting read.