Lisa...I think in your kitchen you could go either way. Regardless of where your (main) sink ends up, it will still be close to the cooktop & you will have room to prep b/w them. If the sink moves to the refrigerator wall, you will have even more prep space b/w them. While a prep sink would be nice, I don't think it's a necessity to make your kitchen work. Yes, it would add an additional prep area for you at the island (b/c there will be a water source) and, possibly, reduce some zone crossing, depending on the location. Right now, to get to the refrigerator from the cooktop you have to either cross the Cleanup Zone or go around the island. How many people will be using your kitchen at once? Will they all be prepping/cooking or will there be a mix of prepping/cooking/cleaning up? If cleaning up is in the mix, then the zone crossing could become an issue, especially when the DW is open. As to location, I like Elizpiz's setup best, but I can see where it would definitely reduce available counter space. If you put it on the left side across from the cooktop, it would be readily available from the cooktop as well as the "outside" part of the island for prepping there while someone else is cleaning up on the "inside" as well as be available for outsiders for a drink of water, etc. However, it will reduce that 42-1/4" to approx approx 24" of workspace directly across from your cooktop; but, as I mentioned b/f, you will still have add'l room on the wall run. If you put it on the refrigerator end, I think you're right in your assessment...I find that I use the counters across from both my refrigerator & ovens much more than the counter next to them...both for removing things from them as well as staging things to put in them. (I have approx 32" b/w the Ref & DR peninsula end and approx 44" b/w the ovens & the end of the "mini peninsula". Both have landing space right next to them as well.) We do have a prep sink, but in our kitchen it was a necessity to make it work. Our cooktop & sink are opposite each other, separated by approx 6'6" of aisle...the main aisle through the kitchen. By adding a prep sink on the cooktop wall, we were able to separate the Cleanup Zone from the Prep & Cooking Zones as well as protect both zones from kitchen traffic (inside a "U" w/short legs but long base). During the week, there are usually two of us in the kitchen...one prepping/cooking (me) and one cleaning up (DH) with an occasional child helping make veggies. On the weekend, there are sometimes all four of us working in the kitchen! When baking (usually a marathon!), there are usually two or three of us. (I seem to bake in spurts...when I bake, I seem to go all out!)

This is not designed to be shoved against a wall. It is designed to have at least 4" of open space against a wall. The vanity is oversized for your location, and it will require opening up the wall to relocate plumbing. Which will be much more expensive than using a standard vanity that dies not require plumbing relocation.

I disagree. I actually have this set up. Our vanity is too small for 2 sinks without looking silly. Plenty of room to brush your teeth or wash your hands while your spouse is at the sink. Also because the faucets are positioned to the far ends of the sink, when you are standing in front of the faucet, there is plenty of room. Michael - it is very useful. I would know.

I'll say single sink 100% of the time. It's just practical, as it allows for drawer storage space; that's more important than a duplicate sink. Go with one nice sink on one side /a decent-sized drawer on the other side. In this case, a 4' vanity cannot support two sinks. Not unless you're talking about those mini-Ikea sinks. As for resale, even people who really want duplicate sinks don't want poorly-designed duplicate sinks.