Notation Interrogation: Figure/Unit Seperation?

This one's just out of curiosity:

When I use a figure like 60Hz or 100mph in an equation, I won't leave a space between the number and the unit abbreviation. However, many articles, datasheets, and other documentation illustrations have no unit segregation. I feel it's my obligation to seek information; so I came to ETO for consultation.

What everybody's recommendation?

My rule is derived from what I would do if I wrote the word for the number. I would put a space between the quantity and the abreviation for units. I find it especially anoying in a case like:

100Ohms.

With the juxtaposition of the trailing zero and the leading O, I'd have to read it several times inorder to be sure.

That's my $ 0.02 USD

In my opinion, a space between the number and the unit is the proper way to do it.