As a long time Smartphone user, I'm really excited about the quality of Windows Mobile 5.0 and most of the feature changes that have happened over the years. But I'll be honest and say that I personally find a couple of the changes we had to make a bit... frustrating. This particular one bit me again today when I missed a call so I decided to post about it now rather than wait for it to come up in the newsgroups after 5.0 devices ship.
In Smartphone 2002 and 2003 we have profiles for "Normal", "Silent", "Meeting", "Automatic", and a few others. When you get a call in Normal, the phone rings. When you get a call in Silent, the phone vibrates. Meeting is essentially the same as Silent. When you're in Automatic, the device will switch between "Meeting" and "Normal" based on whether Outlook thinks you're busy. Cool.
For 5.0, the behavior of Silent was changed so that it is more conservative and completely silent... in other words, Silent no longer vibrates and causes a commotion when the device is sitting on table. If you want to have the phone vibrate when a call comes in, you're now supposed to pick the Meeting profile instead.
Research done by the Shell team (yes, we actually do a ton of user research on these things) showed that this new behavior for Silent is what most users expect and matches up closer to the behavior on other platforms. They're probably right and this will be more intuitive for folks that are new to Smartphone. But if you're a long time Smartphone user like me and keep forgetting to use Meeting instead of Silent (thus missing incomming calls), my suggestion is to go in to Setting-->Profiles and either rename the Meeting profile to "Vibrate" or just change the Ring Type setting on the Silent profile to "Vibrate".