I've heard it's good to put car wax on the bed of your machine for easier FMQ, but do you think it's ok to put it on the Sew Steady plexiglass extension table?

I've never heard of using car wax, and would worry that it might get on the fabric. I have heard of getting a teflon sheet and putting it on the bed (extends to the extension table too) to make sliding the quilt easier.

I wouldn't think it would be a good idea to use "car" wax on a sewing machine. Why would you need to?
Cars have a different kind of paint and are outside in the elements. I don't think sewing machines even have any paint. And are inside, no rain, sleet, or snow. The chemicals in the wax may even destroy the finish on the sewing machine.

It does help on the machine, I don't know about the plexiglass though, maybe try a small spot and see if it helps.

I don't know about the car wax, but I have heard that Johnsons Floor Wax (the kind that comes in the round tins like car wax, not the liquid type) is great for things like the tables of woodworking tools, such as scrollsaws, table saws etc.. it helps the wood slide over the table easier. I haven't tried it with my sewing table though... but as long as you put it on, and wipe it throughly, so there isn't any waxy build up, I don't know why it wouldn't work.

it wouldn't hurt to try, anything to make it easier to slide the fabric on, once it's dry it's not going to come off on your fabric. since the bed is plastic it may not help, I tried pledge, didn't help, the manufacturers should take note and come up with a slipperyer bed!

I revently bought a sew steady table insert for the sewing desk my brother made for me.

On their website it says:
Q: What should I clean my table with?

A: We recommend using Turtle Wax Paste ONLY. We have not tested other products. Use a soft micro fiber towel or soft cloth that does not have any fabric softener or anything that will leave residue and buff until the table is smooth. This works real well and will get the table nice and polished allowing the fabric to slide easily.

Hmmmmmm......turtle was. I would have never thought of that.