Just what does 'Topping from the bottom' mean?

This has long been a hotly debated subject within the BDSM communities; some think the idea genuinely offensive (usually Dom(me)s, others believe it to be a-okay.

The whole concept of T.F.T.B. seems to be a mass of confused description/expectations (just try doing a web-search on the subject!). Some people are 100% adamant that the whole thing revolves around the ability to 'Switch' (i.e., change from sub to Dom(me) either on command or as circumstance dictates). Is this what YOU think?

I've started the above poll just to see if there is a measure of agreement or disagreement on the subject, however it would be nice to read YOUR views on the subject - what you think constitutes Topping from the bottom.