29. A computer-readable storage medium whose contents cause a computing device to specify context data items for logging, by performing a method comprising: displaying a set of available data items; caching values for the available data items obtained from respective data sources; receiving user input identifying a subset of the available data items to be logged; receiving user input defining a logging frequency for each data item in the subset of available data items; receiving user input defining a maximum age value for each data item in the subset of available data items; periodically logging a cached value for each data item in accordance with the respectively defined logging frequencies, wherein logging the cached value comprises: determining an age of the cached value for the data item to be logged; determining whether the age of the cached value exceeds the maximum value age defined for the data item; logging the cached value for the data item when it is determined that the age of the cached value does not exceed the maximum value age defined for the data item; and obtaining a new value for the data item from a data source when it is determined that the age of the cached value exceeds the maximum value age defined for the data item; and determining whether to retain or discard a logged value of a distinguished one of the data items in the subset of available data items based on a determined importance level reflecting the importance of retaining the logged value of the distinguished one of the data items in the subset of available data items, wherein the determined importance level is specified by user input.
30. The method of claim 29 wherein the computing device in which the method is performed is a general-purpose mobile computer system.