I have recently migrated an Exchange 2003 front end/back end environment to new installs of Exchange 2003 front end/back end in VMWare. They are now on quad cores with 4 gigs of ram each VM. My users are now complaining that their Motorola Q's are beeping, only to find no mail. As it turns out, their devices are seeing new mail before rules are applied that move them into folders or junk mail.
This is annoying because they are support techs that are required to answer support emails within an hour 24X7. Every junk email or mailing list is getting them out of bed at 3 am only to find an empty inbox. They are blaming VMWare causing Exchang's reaction time to slow. Tha's bad because when I found them they were in the stone age.