When Should Indexes Be Rebuilt

Richard Foote has written an excellent presentation on Index Internals and Rebuilding of Indexes.

Using an Index for a NOT EQUALS Query

Lauerent Schneider has posted an example of when you _can_ use an Index to drive a NOT EQUALS query.

Always Explicitly Convert DataTypes

Good programming practice [whether in Oracle or any other software environment] is to NOT rely on implicit conversion of datatypes. Particularly if you are working with multiple languages. Also, when you go through an upgrade to a new version.
Tom Kyte always recommends Explicit Conversion of DataTypes. However, he acknowledges the occassion when he did not follow his own advice -- and he was embarrassed in front of his audience.