I haven't dared to try Outlook 2007. I've heard some frightening stuff about its performance… and since performance is somewhat important to me, I,ve decided to stick to Outlook 2003.
I've tried to use many other organizers/PIM/Todo managers (trialed them or used them for a while : DoOrganizer, Essential PIM, Achieve Planner, Chandler, Anytime Organizer, Info Select, Sunbird, Thunderbird, TimeTo, SQLNotes — IMO very promising —, Todolist, My Life Organized, Calendarscope, Vitalist, Remember The Milk, etc.) but I always come back to Outlook. Some of the reasons are : Palm syncing is mostly flawless, it’s pretty customizable (forms, columns, fonts, colors, etc.), it interacts well with many other application (even with farr!), it’s searchable with X1, Archivarius, and a bunch of other desktop search programs, etc.
So, I generally do like Outlook 2003 and find it pretty reliable. Except (mostly, but not exclusively) for :
1- The absence of any small integrated project management tool (I know that there is Microsoft Project ; but 1- MP is not even completely compatible with Outlook — the different tasks fields don't transfer and synchronize properly… and, anyway, 2- I'm not asking for something as complex as Microsoft Project to take care of all my small projects…);
2- (in relation to my first point) Outlook’s tasklists inability to support “sub-tasks” — what a nightmare : you can’t subdivide bigger tasks into smaller steps, unless you devise your own system (I did : not exactly optimal, but it's okay) or use a plug-in (apart from the GTD add-on and Gantt for Outlook, anybody here has a suggestion?);
3- Outlook’s very basic (almost absent) prioritization system (it’s possible to circumvent that too, though, with a bit of imagination : Outlook forms are very flexible : you can rename any fields you want and fill them with your own parameters, etc.). A nice algorithm to calculate task priorities would also be cool also… (is there a plug-in for that?)
4- Outlook’s so so management of recurrences and rescheduling (I hate it when it duplicates tasks after changing the recurrence);
5- Outlook's lack of a vision or clear "organizational philosophy"... (this is actually a bit of a strength at the same time : it might make Outlook more flexible)
And some others, of course. But these are the main ones I can think off, quickly… actually, these reasons alone probably drive me crazy enough to make me want to switch to another application every month or so! Many other applications will solve my tasklists/project management problems, but, unfortunately, will often add other problems that are usually even worse (IMVHO, of course);
If one is using a GTD approach or any other more sophisticated organizational system (project oriented, maybe) with Outlook, one has to figure out a way to implement it... almost from scratch. It took me a lot of time to have Outlook behave the way I want, synchronize with my Palm effectively, etc. — and I'm still not completely satisfied.
Achieve Planner could be an interesting Outlook replacement for those who are into GTD and/or Covey’s philosophy (I'm keeping an eye on it). But the last version doesn't do e-mail (that, I could deal with, I guess, and use a dedicated email program), doesn't synchronize directly with the Palm, is not searchable through X1 or Archivarius, doesn't have a very powerful and flexible search tool, etc. etc. And these are all aspects that have become really important to me.
Sorry for that long post... I guess I'm procrastinating.
[edit : corrected 2-3 stupid mistakes]