Fortunately, Sony made an optional EVF for the NEX-5N, the FDA-EV1S external viewfinder. Unfortunately, it's not cheap; it costs slightly more than half of the NEX-5N with a kit lens. I bought mine used from Adam, but it was defective. Took it to Sony's repair center and I was given a brand new one. Haven been using it for about two weeks. Below is my impression of using it.
Bleeding Hearts -- NEX-5N & Kodak Printing Ektar 93mm f4.5. Click for larger.
Without doubt, the EVF helps a great deal in a few areas. It addresses the biggest issue of unreadable LCD screen in the sun. Another advantage is when using long lenses. The EVF helps to stabilize the lens and thus reduces handshake. These are the major concerns that I have, and the EVF does its job well.
It's not perfect, of course, and this is not even taking into the account of the high price. First of all, there is no locking mechanism on the adjustable viewer. Very frequently, I find my glasses pushes the eye piece and moved it upwards, when I really want to see horizontally. This annoys me a great deal. Secondly, I find the image inside the viewfinder to be of very low contrast, which makes it very difficult to focus on something that's not very contrasty. In this aspect, I find the EVF on the G1 much better for manual focusing. Lastly, light leaks too easily into the viewfinder through the eye piece. Again, the G1 has none of this problem, because the eye-piece is very large and soft that forms to the eyeglass. The eye piece on the Sony EVF is very hard and small, compared to that of the G1's eye piece. The blocked up shadow area problem that many people have, is not too much of an issue with me. I am actually OK with it, but the three problems listed above just bothers me. I guess if you don't wear eye glasses, you have fewer problems.
Despite the issues I have with the EVF, I find it indispensable for shooting in day light, or with longer lenses.