What I like about free WiFi in the lobbies is you know that a hotel is going to have reliable access somewhere when you book it.

Plus, I really like knowing that if you need to go to have a meeting in lobby, or quickly check email, etc, you can do so at certain hotels.  Like "oh, there is an Omni, I know I can get WiFi in the lobby."

That said, having reliable free access in both the lobby and in your room is the way to go.