If you recently updated your Palm Pre or Pixi to webOS 1.3.5, you should upgrade to the latest version to be pushed out. Version 1.3.5.1 only contains a single bug fix that had been introduced with the previous release.
This release fixes an issue in which the Calendar app displayed no events for any account after a user synchronized Calendar with an Exchange account. With this update, Calendar events now appear correctly after an Exchange sync.
So far, the update is available to Sprint users only. In Canada, the latest version of webOS to be available is the older 1.3.1.