jkOnTheRun's Kevin Tofel understands my pain. While grateful that the existence of Exchange and its various clients allows users to have access from multiple devices to appointments and tasks without having to spend a lot of time getting the information synchronized to each device, like me, he wants more. Then again, I should probably say we want less, as in less time spent dismissing reminders on our various clients.
You see, if I create an appointment or task on one client and specify a time to be reminded of my appointment, then all clients which connect to my Exchange account will remind me at and after the appropriate time...even if the event has passed and I've dismissed the reminder on one of the clients. Dismissals don't sync. So what, right? I'll tell you so what! When the PC at work, the PC at home, the Tablet PC, the UMPC, the Pocket PC phone and Exchange On the Web Access are all reminding me about the same dadgummed thing, and each device has to be told not to keep reminding me about it, well, the efficiency kind of stops right there, especially when it comes to my tasks (a new reminder is likely to make me wonder if I forgot to do something I've already done).
Like Kevin says, it's time for reminder management to be handled at the server level. I look forward to the newer, better day.