Higher PR often seems to help a site get more frequent caching. Of course, that's a long-term answer and not an immediate fix. I would say check your logs for the most recent googlebot requests and make sure it's getting a correct response. In the short term that's all that is within your power.
In recent days, Google seems to be slow in updating the cached page for many. Even though server logs show a googlebot request 4 or 5 times since the cache date, the cache still seems stuck. This is not normal behavior, and it might presage some kind of significant change. Guess we'll all see soon enough.