Of course, I'm forgetting the strangeness of water - thanks for the reminder on the contraction!

I googled and found this interesting piece about Chandra...

http://cxc.harvard.edu/newsletters/news_12/chandra_ops.html

"Hydrazine contracts as it freezes. This allows more liquid to flow into the resulting void and also freeze. When the lines subsequently warm up, they are not expected to thaw uniformly, so that the liquid expands against the remaining frozen "plug" and stresses the walls of the pipe. In ground testing, repeated such cycles have been observed to eventually split the line. It is impossible to analyze the exact consequences, but obviously release of such a contaminant into the Chandra HRMA or equipment volumes could have disastrous consequences, and must absolutely be avoided."

And on Ulysses

http://science.nasa.gov/headlines/y2004/17mar_ulysses.htm

"About eight meters of fuel line snake through the spaceship. Every twist and turn is a possible cold spot, a place where the hydrazine can begin to solidify. "If the hydrazine freezes anywhere, I don't know if we can safely thaw it again," worries Castro. When hydrazine thaws, it expands, possibly enough to rupture the fuel lines. Ulysses' propellant would fizzle uselessly into space."

most appropriately, Emily cited Deborah Baas's blog entry about this very issue

http://www.planetary.org/blog/article/00001034/

http://ippw.jpl.nasa.gov/20070607_doc/8_21MEHT.pdf covers the physical impact of thruster firings on the ground