I know this isn't "gardening", but you guys are green-thumb plant gurus, and that's the type of knowledge I need \:\)

My back yard has never been treated professionally for any kind of weeds. The front yard was prior to us moving in 4 years ago, and I've been able to keep it looking OK with do-it-yourself treatments that have saved a bit of money.

I assume that the desirable grasses are dormant by now in the back yard (it looks like all the green stuff is johnson grass, monkey grass, clover, dandelions, or stuff I don't know the name of). Is there a treatment method that I could use now that would save me a lot of headache in the spring?

I've heard stories of people putting Roundup on the yard in December, and it only killing the active/green weeds and leaving the regular grass alone. Is that true?

What do you guys recommend? If it matters, my back yard is pretty small (1/8 acre I guess).

I'm hungry and tired. Don't poke my belly.