Watching the "Alien Planets" episode of the History Channel's Universe program, we learn an interesting discovery: planets around a pulsar (for example PSR B1257+12). That should be impossible - a pulsar is what is formed after a massive supernova explosion, an explosion so powerful that any planets should be destroyed. However, three small rocky planets were found. What they now hypothesize is that these are planets that formed from the debris of the destroyed orignial planets. If this is so, then this is more proof that planets can form even under extreme conditions; gravity wants to clump debris together, it is a natural consequence of matter and gravity. Thus, planets are probably very, very common.
By the way, life on a planet around a pulsar is very unlikely - there is far too much radiation flooding the system, especially if the planet happens to be in the way of the emission beams from the pulsar's magnetic poles.
Pennsylvania State University. "Scientists announce smallest extra-solar planet yet discovered." 10 February 2005. 29 November 2007. <http://live.psu.edu/story/10180>
Wolszczan, A. (1994). "Confirmation of Earth Mass Planets Orbiting the Millisecond Pulsar PSR B1257+12". Science 264 (5158): 538 – 542.