This is a popular question, so I'm including just two recent threads on this topic:
Besides reading the reviews here, one of the better ways of gauging if an Inn is a good "fit" for you is to call a few places, and ask them some questions. What restaurants do they recommend? What type of person stays with them? And what kind of services do they include with the price of the room? (This last one's a biggy).
In this day of email and internet web sites you can literally plan your entire trip from your PC. This is convenient, and saves lots of time (and money on phone calls), but websites can be deceiving.
In most cases, calling 2 or 3 places will give you a good idea what is the best "fit" for your personality and needs. One may be too friendly, while another might be too impersonal. Finding a good spot is part research, part luck, and part interview.
Even if you hate to call, please give it a try. You will be amazed at what you hear!
July is a lovely time to visit Napa. It's sunny during the day (80-90s), but never humid. The cool evening breezes (it goes down to 55-60 every night) are absolutely wonderful.
And four days (July 8-11) is a perfect amount of time to really discover some of the hidden secrets this Valley has to offer.
I hope you have a great time! :)
Napa Old World Inn