Just wanted to draw your attention to the following article if you use S/MIME through OWA:

The Outlook Web access (OWA) form stops responding after you install Internet Explorer 7.0 and the S/MIME control on a client.

The update is live at:

http://www.microsoft.com/downloads/details.aspx?FamilyId=41275DEC-4C01-4C41-AA64-C9DBE5EA3F7E&displaylang=en

The associated KB# is 924334