I don't have any experience with the Nemo either. I have experience with zip together bags (from REI) and much prefer my Enlightened Equipment quilt. Tim from En. Eq. previewed on facebook a two-person quilt he is developing. It probably won't be on his website until July, but if truly interested he would probably make one for you before they go up for sale on the website. Jacks r Better also sells a two-person quilt.

My zipped together bag works nicely but is much heavier than a comparable quilt. My advice if you get two bags that zip together, get two different temperature ratings. That gives you more flexibility. You can put either bag on top depending on the temperature, or put the zipper between you and your partner if you have different insulation requirements.