For couples who are currently going through a bad patch, this cookbook will probably just make things worse: it requires a lot of cooperation and a sense of humor.
For couples who are competitive with each other, you might not like the results when you get out of sync with each other on the instructions because one of you was trying to do his/her part better or faster or with more seasoning. (Not that I'm speaking from experience!)
For couples without access to a well-equipped kitchen, you will be frustrated by the equipment and ingredients that you don't have. This book doesn't require anything really exotic, but it sure is a lot easier if you have lots of different types of pots and pans, a food processor, stove, oven, microwave, and plenty of timers.
Aside from those caveats, you really can't go wrong. The instructions are spelled out in detail, so that even couples without a lot of cooking experience can create complex, exciting meals together without running into the timing pitfalls that usually plague beginning cooks.
Enjoy -- and better clean up the dishes as you go along, because you'll probably be in too romantic a mood to wash dishes by the time you're done cooking, eating, and drinking wine!