I used Norvig's frequency counts as input for the board generation algorithms (in Scala) for my Android word game "5 Star Words" [1]. With this as the start plus a few other tricks, I'm typically able to reach an average of ~300 common English words (or easily 400+ when including less common and swear words) on a 4x4 letter board.

[1] https://play.google.com/store/apps/details?id=com.starwords