A float is a float is a float?  Totally unreasonable assumption :-)

Two things to consider:
- If it goes as 2.1E-6, the Model_Item validation will bomb (which is how I noticed it).  This can be rewritten, of course.
- Does MySQL like making comparisons with floats?  In other words, if we ask it to find < 0.1, will it find 0.0000021 and 2.1e-6?