You can find the full changelog for 1.7.1 at this page:

Here is a summary of the note-worthy fixes and changes in 1.7.1:
- fixed for broken challenge/response feature (temp workaround)
- fixed bugs in the email validator that caused a good number of people not to be able to register (terence)
- updated translations (thx to many translators and devs)
- page description is used on the "view category" page instead of wiki page source (sylvie)
- HAWHAW has been updated to stable v5.1 (nhuffschmid)
- many HotWords fixes and enhancements to make it work as expected (terence)
- the categorize list in edit pages shows full category path now (mose)
- some LDAP authentication fixes (lueders and others)
- fixed various forum thread action bugs (terence)
- avoid caching URLs with common binary file extensions (terence)
- various theme and visual fixes (gimpster, mose, zaufi, ohertel)
- added many TikiHelp links (dgd, terence)

Onwards to 1.7.2, 1.8 and beyond!