Yes, I have one. It supports a 30" fireclay, farmhouse sink.

That is what the cabinet person at Menard's recommended to me, too, and I questioned why so big. he had good arguements for it that I have forgotten now. I still haven't decided if I will go that big for my 30 in. farm house sink. I have plenty of time but the rest of the cabinet layout depends on what I do there. Does anyone have any more input on that? I wouldn't mind going to 36 inches. Would I be sorry for going smaller? I plan to put a trash pull out on one side even though it will be small, it could work. Under sink space is such a waste, I hate to have more of it than necessary.

I did a 33" sink base for a 30" farmhouse leaving 1 1/2" on either side--it looks nice

maybe the design works better with a 39" sink but if that's the case i think i would still do a 33" with 3" on either side for decoration like flutes or legs or split posts or something

My sink base was that large only for reasons of design symmetry. In my galley style kitchen, the range and sink face each other across the aisle. Since the range is 39" in width, we installed a sink base cabinet of equal width -- even though the sink itself is only 30". I love the extra large base cabinet, but it was not necessary for proper mounting of the sink. I'm sure you can get away with a smaller base cab and it will still function and look good -- as Pence notes.

Do you need the full 39"? If so, then go ahead. But, if not, as Pence said, I'd go with the minimum you need. If that means 6" less and you're going for symmetry, I'd put in a 3" filler pullout on either side w/a decorative "leg" front or similar or a plain panel, depending on what goes better w/your kitchen style. My personal opinion is that the filler pullouts will be more functional than that extra 6" of sink base since sink bases generally do not give you the best use of space.

Check out Alku05's filler pullouts flanking her cooktop in the thread linked below to see what I mean.

Here is a link that might be useful: Thread: Rev-A-Shelf Spice Racks for Fillers -- Have you seen these!!!!

I have one, for my 36" Shaw's sink. With the trim-out and the