Outlook: embarrassment
I'll be among the first to congratulate Microsoft for doing a pretty good job - writing software that's stable and reliable in the wild is very difficult, and all of their software works with most of their software most of the time. This is considerably above average performance and rather more than the Microsoft-is-evil crowd has ever managed.
However, Outlook is, or at least should be, an embarrassment to Microsoft. I realise it's more than just an email client. I know it does fancy calendaring and it consolidates a plethora of mail providers. But 100MB memory footprint is just plain silly.
The ridiculous memory consumption I can ignore - I have equally ridiculous amounts of memory installed, so it isn't really a problem. But there's another defect, and it is rather more serious since it affects other software. Outlook frequently stalls the global message queue. As a result, it interferes with any software that uses the shell common dialogs (just about every program ever written) and it interferes with debuggers.
At work I have a running battle between my boss, who insists that I run Outlook all the time, and my boss, who wants me to debug software, an activity not assisted by Outlook.
There is a workaround. It depends on having scads of system resources. What you do is run Outlook in a virtual PC. This isolates the antisocial Outlook from the rest of my PC.
Arguably the mere fact that this problem can exist implies severe design flaws in Windows messaging, but this is hardly news and is a situation unlikely to improve for legacy reasons.