Hah! If Mike Cowlishaw was here he could give you a wonderfully eloquent treatment on why binary floating point sucks. And he's actually done something about it [1] with both a format and software to deal with decimal numbers.

Further the densely packed form gets very close to optimal in terms of bit representation. Assume that 4 bits (BCD) is 'worst' case, you can represent 0-9 but you 'waste' the information space 'a-f' (in hex, 10-15 in decimal) but 3 bits only gives you 8 states. What you want is a total of 10 states which is 3.3125 bit's worth (best case) or 3 digits in 9.9375 bits, these formats give you 3 digits in 10 bits which is pretty close.

Mike goes on to talk about how to build hardware that does floating point operations on this stuff. I built some into an FPGA and it really is pretty straight forward, especially if you do iterative multiply and divide.

Consider the interesting thing where you take 128 bits (two 64 bit words) where you use 60 bits for the whole part (18 digits) and 60 bits for the fractional part (18 digits) and you've got 8 bits left over for various non-number entities (+inf, -inf, NaN, etc). Would be great for CAD package, or a financial spreadsheet.

[1] http://speleotrove.com/decimal/DPDecimal.html