I've been using My Life Organized (MLO) for Getting Things Done.  Since it is really just an outliner that can synch with Outlook Tasks, I thought I'd take a look at the general category of outliners.

Things I want from an outliner:

• Expand/collapse branches of the tree
• Brain-dead easy to use
• Works on (or synchs with) iPhone, Blackberry, and Windows Mobile
• Works on Linux/Windows/OSX

Things I'm not sure of:

• Web or desktop?

Interesting candidates:

• My Life Organized
• LooseStitch
• Sproutliner
• iOutliner
• Bonsai

Yes, I'm aware than none of these meet my iPhone/Blackberry/WindowsMobile requirement or my Linux/Windows/OSX requirement.  If you find an outliner that does, please let me know in the comments!

Issues and observations:

• My Life Organized
• It is what I'm using at the moment
• It is focused on GTD (this is both a plus and a minus)
• Desktop application
• Synchronizes tasks with Outlook 
• Does not do OPML 
• Can be used to capture task time (start/finish dates, time on task, etc.) 
• Retarded about Alt-F (press and release Alt, press and release F)
• Handles the context menu button on the keyboard
• Generates alarms/reminders when a task comes due
• LooseStitch
• Web based
• I can't find a way to list all of my outlines (7/15/2008).
• Sproutliner
• Web based
• I can't find a way to list all of my outlines (7/15/2008).
• iOutliner
• Web based
• I can't find a way to list all of my outlines (7/15/2008).
• Bonsai
• Feature-complete, general-purpose outliner

• Desktop application

• Synchronizes with Palm 
• OPML support 
• Does not handle the context menu button on the keyboard
• Does not generate alarms/reminders when a task comes due

For all the web-based outliners, I'd need a daily export in order to protect myself if they summarily shut down their web site.  For desktop applications, I'd just need to add the data files to my pre-existing backup process.  Web-based outliners come closest to running on Linux/Windows/OSX/Blackberry/iPhone/WindowsMobile, assuming I use the web interface from the cell phone.

I work for a company with pretty restrictive web filtering.  At the moment, I can get to the online outliners, but there is always the risk of being cut off.  For the web outliners that are open source, I could always install them on my server, but that is geekier than I want to go for an outliner.  Of course, if it isn't web, at the moment, I can't get to it when I'm away from my desk.

Tentative Conclusions:

• I'm going to use a desktop application, because the risk of non-access to web outlines is too great (in my situation).
• OPML is a big deal, because it lets me exchange data with other outliners.  You can export from MLO, but it takes some massaging to get the data into another outliner.  Advantage Bonsai.
• If I had a Mac at work I'd use OmniOutliner Pro.  I could use OPML to do OmniOutliner at home and Bonsai at work.  Advantage: Bonsai.

• Alarms (reminders) are a big deal, because they prompt me to take action.  Yes, I can create a separate alarm in Outlook, but that is an additional activity.  Not only does the due date in Bonsai not send an alert, it is a due *date* and not even a due date-time, so I can't even graft alerts onto Bonsai.  Advantage MLO.
• MLO works well for GTD, but Bonsai is a better general-purpose outline (IMHO).  I'd like to use one outliner and not two.  Advantage: Tied.
• MLO will synch with Outlook tasks.  This is important because I can drag an email to my Tasks folder, and add a to-do with the email body as reference.

It comes down to -- do I want a better general-purpose outliner, or do I want a better GTD tool most? 
I'm going to use MLO for GTD, and Bonsai for other outlining.  I love the idea of using fewer, general-purpose tools, but in practice, I keep using more special-purpose tools because I keep hitting must-have features.