I look after computers for a lingerie company and they have Office 2007 on 2 PCs and 1 lap. Outlook 2007 broke after using CCleaner. But a re-install fixes it.
Outlook 2007 has 2 major optional plugins which change the way the program works.
The first is Business Contact Manager (BCM), which ships free with Office 2007 Small-Business. BCM uses sql-server to share contacts with other computers also running Outlook BCM. It is quite fiddly, and can break the karma of the unprepared user, with some-times niggly bugs. If you get it stabilised, and leave it, it seems to run a bit more smoothly. Installing BCM (which is still in beta I think), makes some major changes to the Outlook facia, (well, a new folder called Business Contacts, and a new menu header with same name). The BCM contact entries have more business-style fields than the regular Outlook "Personal Folder File" (PST). The BCM contacts are stored in an SQL database, so Outlook suddenly uses multiple technologies to store it's data.
The second plug-in to worry about is Microsoft Office Accounting 2007 (MOS), which again is in beta. This program also uses SQL databases. MOS has an option to integrate with Outlook's BCM. The result links MOS financial history records to your customers in BCM. So when viewing business contacts in Outlook, you can click on a new button Financial History, and see what they have bought off you previously. Quite useful, but again, a little tricky for the unprepared, but a geek understanding of Microsoft networking may help get it working.
The problem with CCleaner was that Outlook stopped responding. The PST view came up very slowly, and the BCM view came up not at all. It may be an issue with the SQL side. I believe (hmm) the problem also occurred when the Office section of CCleaner was disabled.