If you own a boat/motor that is valued at $7500 or more, it is subject to a luxury tax. The milledge tax rate varies from county to county. It is .0282 here in Bartow county.
They assess the tax based on 40% of the current NADA or Blue Book value of the boat, each year. If you own two boats/motors the combined blue book value of both boats is assessed for the tax. If your boat is valued at $24000, 40% would be $9600, then applying the .0282 rate the amount would be $270 for this year.
Hope this helps, I agree it sucks!

When did they start that??? That's a lot of B.S.

It's always been that way. I had to pay the tax until my boat aged enough that they quit sending me the form.