I have currently been using Doit.IM for 10 days, daily and extensively. I am absolutely loving it.

A) The best things about DoIt.IM
1. Quick Add
A major advantage of Doit.IM over other systems is the ability to quick add tasks in the web interface and also on Android. I work at my computer 99% of the time (I'm a website manager) and have an Android tablet and Android Phone. The Quick Add is essential for me: when I rember something to do, or have an idea, I can very quickly jot down tasks. Thanks to the Inbox, I also don't have to think about where to put it, I can do that at a later time.

2. Offline & Sync
Since I'm not always online, it's great to be able to use Doit.IM offline and then sync once I am connected again. Somehow the sync works just the way I want it to, I can imagine that must be quite a feat.

3. The web interface
The web interface is really great, not a dumbed down version of the app like a lot of other solutions. I like the fact that it works in all browsers, my favorite are Firefox and Chrome. It has all the options, is really fast and has very nice transition animations.

4. Send mails to DoIt.IM
Since a lot of tasks are assigned to me through mail, and I also often (implicitely) assign tasks through mail, this is an amazing feature.

5. GTD centric
Even though I never read the book, I still feel the system is intuitive enough to get started with right away.

B) Feature requests / suggestions (in no particular order)
1. Larger Font Sizes in web lay-out, for example by using a font size slider
2. Move subtasks above description/comments field: often I send a mail or paste a longer piece of text, which moves the subtasks all the way down. I wonder if it wouldn't be better to move subtasks to the top, above the description field
3. Theming support for web layout: for aesthetics, but also for higher contrast between background & text
4. Ability to edit subtasks just like you can edit regular tasks, with all options of regular tasks including comments. For reference, the main task (+link) is always shown together with the subtask.
5. The possibility to select text in description and comment fields and create subtasks from them. Useful when forwarding mails or pasting text which contains several tasks within.
6. Some sort of notepad in the web lay-out where you can temporarily put notes / text. Or is that what inbox is for?)
7. Quick add tasks: possible to add dates AND time in human-readable format, e.g. ^15PM = 15PM today. ^Friday = friday this week ^Next friday = friday following week ^Thursday 15PM = Thursday this week, 15.00PM. Similar to how Astrid does this
8. Integration with Tasker (the Android app), e.g. it would be nice to show only my home tasks when I am at home.
9. Possibility to delete comments
10. Better "Focus" mode, e.g. only focus on / show "do it now" items
11. Support for attachments: own storage OR send to evernote account and create a link in the task.
12. Search also searches text in subtasks
13. Possibility Create links to existing tasks and also to websites
14. "Templates" for regular activities; special "flowchart" screen for regular task workflows.

For example "receive error report" => "request screenshot" => "report bug" => "keep an eye on bug (warn me in 1 week) ==> "mark as closed". You can drag your task into a box, pick from a number of arrows and enter a number of settings (due date, notification, ...)

C) Some remarks about blog&updates
It's probably just a coincidence, but the last blog posts are all about the Mac version. Using Windows at work, Android on my tablet and phone and Ubuntu at home, I'd like to read some news about the versions other than the Mac version. And also, not just release notes:
- how are we improving DoIt.IM?
- What features will be adding?
- What's new for the web version, Android version, ...