The comment about the 2gb PST file size limitation only applies to ANSI type PST files. ANSI type PST files were created by Outlook 97-2002. Many people used their old Ansi PST files with Outlook 2003, 2007, and 2010 and so may face the 2gb maximum file size limitation (as will as maximum message counts for each folder). For offices that do not have exchange server and may have multiple ANSI type PST files that they would like to convert to Unicode type PST files created and used by Outook 2003, 2007, and 2010 and which do not have the 2gb limitation you will appreciate an amazingly effective and inexpensive utility from Peter Maclean called Upstart. It can be found here:
http://www.maclean.com/upstart.phpIt is a must because hitting the 2gb limit can happen without warning and can result in data loss if you do not have a recent backup of your PST file to fall back to.
Upstart makes converting a breeze.
But having said that, it generally is a good idea to keep your PST file, even a Unicode type PST file, as small as possible as corruption can strike anytime and it becomes very time consuming to repair large PST files. Configure Outlook to utilize AutoArchive to push older items off to an Archive PST file (a secondary PST file) as a simple way to keep things under control.
Good luck.