Microsoft Outlook is a great, shambling, brute of an application. In the fold of Office it has obliterated all traces of its betters, it stands unchallenged atop a mountain of the digital dead.
The beast is encrusted with the weapons of forgotten wars. Many barely work. Outlook 2003  still lacks a cross-PST accessible object identifier, so neither Microsoft nor developers can create a robust object link. Sorting a categories view still undoes the view settings -- a bug dating back the 90s that was only fixed in Outlook 2007. Outlook 2003 tags (categories) are still stored in the registry and the master category list has been utterly broken since the dawn of time (happily, it can be ignored).
All the same, in a stupid and accidental sort of way, Outlook is powerful. If you can figure out where all the sharp edges are, if you learn to step around the explosive charges, if you have good backups and you know all the command line repair utilities and the caches and configuration files to periodically delete, it can be sort of tamed.
I have, over the course of many years of trial and pain, figured out how to make the combination of Outlook and Windows Desktop Search work. Yes, it periodically blows up in a very impressive fashion, but that's life with Microsoft. Only Excel is immune to this behavior.
The combination of full text search across GB PST files, the ability to effortlessly rename email subject lines, drag and drop transformation from one type (ex. email) to another (ex. task), the quick tag (category) and the ability to set metadata (category, due date) values by dragging and dropping between view "headings", the robust metadata query language and hierarchical view srtructures -- put them all together and one can painfully create a semi-stable workable PIM environment.
It only took years of work. I could write a book, indeed I've taught around a draft of such a book in my corporate life.
Apple could do far better -- if they wanted to. I don't think they want to. Microsoft could fix Outlook , but I sincerely doubt they care. There will never be a challenger to Outlook on a Microsoft platform. Google now ...
Well, I can dream.
Which comes, at last, to what I want.
We all know that managing work by email is the road to damnation. Work must be managed to tasks, which in Outlook are created by renaming subject lines  then dragging and dropping email to the task icon. Tasks get priorities, and depending on priorities they may be assigned due dates, calendar slots, and category attributes.
The process of creating these relationships between task, email and appointment could all be made much more fluid, but I'm asking for less than that. All I want is a quick way to find tasks based on the subject lines of incoming messages. Then I can update existing tasks rather than creating new tasks and then resolving the redundant tasks.
Put a button next to the subject line -- or on the email taskbar somewhere. When I redo the subject line  I'll click the button and the application will run a full text search using WDS to locate matching tasks. I'll then select the task I want.
I think an Outlook developer could probably do this. I'll pay $30 for this feature.
Go for it.
 I've used Outlook 2007 a bit, but we're still stuck on 2003. My sense is that 2007 has fewer bugs but probably no significant new features.
 I am running a one person campaign in a large publicly traded corporation for better subject lines. I think it's slowly working, but for the foreseeable future being able to effortlessly redo subject lines by clicking and typing in the subject field will remain one of Outlook's best features.