I have used Wallpaper* guides for other cities and with a trip to Paris coming up, it seemed worth going for the 2011 guide for that City.
These guides really are brilliant and this Paris one is no exception, featuring some of the most newly opened and (apparently) hip places to go to in France's capital. If you want a street-by-street guide (with a map showing similar detail) and a discussion of the historical places to visit, then this guide probably won't do the job, but if you are keen to have a good time, see something slightly different and stay/eat in cool and unusual places, then the guide really is essential. I wouldn't say that the guide is that useful once you are on the trip but I did find it very helpful when planning beforehand. That said, the Wallpaper* guides are so small and portable that they are probably the easiest thing to take around with you. Bring updated on an annual basis as well gives the guide a fresh and relevant feel.
Although I've supplemented this guide with plenty of follow-up Google searching and purchasing more specific guides (Zagat and Michelin), the beauty of this is that it is broad enough (i.e. not just a food or hotel guide) - it really does cover enough of everything.