Soon after switching to Mac I discovered that one of the myths that I lived with for many years, i.e. that Adobe Acrobat Reader is mandatory in order to view PDF documents, is no longer true.
As in most cases, Apple did a great job integrating its own PDF viewer in the system application Preview.app; it is lighter, looks significantly better and integration with the rest of the system is great.
I do not suggest to completely remove Acrobat from your system, you might encounter documents requiring special features not yet implemented in Preview, so leave it to dust in a corner and configure Safari to not use it as default.
For this you have to prevent Safari to load the Acrobat plugins. These are special OS X components, stored as special folders in /Library/Internet Plug-ins.
There might be many ways of doing this, one of them being to move them to a separate folder.
cd /Library/Internet\ Plug-ins sudo mkdir Disabled sudo mv AdobePDFViewer*.plugin Disabled
On OS X 10.7 Lion, there are two files moved, AdobePDFViewer.plugin and AdobePDFViewerNPAPI.plugin.
After moving these files, restart Safari and when opening PDF documents the internal Preview.app will be used.