The HTC Messaging client is well know for being slow and buggy, such that many ROM cooks now intentionally leave it out when producing new Sense ROMs.
Those days may be over however, with a new build of the infamous software leaking out. Version 1.8 is not only faster and more stable, but also includes a feature I believe unique in a shipped OS â€“ hidden SMS messages.
The so called Secure Box feature allows some SMS messages to be password protected, meaning some Lotharios will not have to hide their phone as much anymore
The cab for the new build can be downloaded in this XDA-Dev thread, but may not work in all cooked ROMs.