> I'm using 10K successfully right now.
> 
> I can't see where I2C hardware problems could cause hangups

If the pull-up is too high for the buss capacitance, the signal transition
times will fall outside I2C spec. Your 10k implies a buss C of 75pF
according to Section 16.1

303kB

http://www.semiconductors.philips.com/acrobat/literature/9398/39340011.pdf

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