what is this search about
http://www.google.com/psearch

Search History stores what you searched for.

Personalized Search uses what you searched for and which results you clicked to personalize your future search results (which you can turn off by clicking the "Turn OFF Personalized Search (Beta) for these results »" link in the top right if it's in use).

I think Google kind of merged these two services a while ago so that if you have Search History enabled, Personalized Search is automatically enabled too.

Read the help files for more info:
http://www.google.com/support/bin/topic.py?topic=1593