Brainstorm

The Notification should appear throught a right-ward extension of the status bar (where battery/ reception is shown).

This will simply add a little section to the box with symbols like an Envelope with a small number , or Telephone with a small number.

This way it is available on all desktops.

You mostly miss calls, smses, mails and so forth when you are not using your device and the screen is locked. When the screen is locked is also when it is most inconvenient to check the notifications. If you just want to check what you have missed you have to unlock the screen, switch to the dashboard and then presumably lock your screen again and continue doing what you were doing.

I propose to have a summary of missed notifications on the "slide to unlock" screen. That way you are just one click (on the power button) away from it and don't need to unlock and re-lock the screen. You might be checking the time that way anyway, so it feels natural to have other "quick access information" there. Things like next item in the calendar could actually be convenient to have there as well, but I guess that's a different brainstorm.

The notification LED is useless when the phone is in holster or pocket.  A widget or built in feature should exist where the ring tone/beep can be selected for each (SMS, Email, Voice Mail, Call etc) and the frequency of the reminder 5, 10, 15 etc minutes.  There are time when these events occur and the phone is not in hearing distance (in the shower for instance).  This could be an extension of the notification LED.

Currently it is too easy to forget about SMS, missed call or voicemail notifications as it is easy to dismiss the desktop notification and move on to something else.  This is due to the lack of persistent status or notification icons for the missed event.

I would suggest using the status bar icons area and add in some kind of phone control icons that would show phone status, for example:
1) Voicemails
2) Text messages
3) Missed Calls

This could be extended for emails also but initially I think it would be most helpful to use for phone functionality as when you clear the original desktop notification it is easy to forget about the event.  The status area of the n900 is currently the one area of the phone which contains the same persistent set of icons, if this was extented with phone status icons it would be the most useful I think.

This would follow other phone OS's where any missed event notifications appear in the status area - symbian 5th presents these icons on the stop status area of the display (this is also the same for Apple and Android). 

You would then be able to drop down the status area and click on the phone notification button to open a separate window which would show the details about each individual phone event.  Clicking on these events could then take you to the applicable application, for example:
* Clicking on a missed call event would take you to the phone app and dial the number.
* Clicking on a voicemail would take you to the phone app and dial your voicemail
* Clicking on a text message would take you to the conversations application

Once you clicked on the button and drilled down into the missed events the event icon would then be removed from the missed notifications.  This way you get a persistent notification until you take the required action so you will not forget about them easily.

This could be implemented as a widget that installs into the status area similar to the screen brightness widget or the load-applet which installs the interactive charts for cpu and memory into the status bar but then also adds the screen shot or video buttons into the status buttons.  Same for the Availability IM button, you have an icon showing whether you are online or not but then clicking on the Availability opens an additional "My Availability" area - this could be the same for the phone activities.

Regardless of where the notification is, dashboard or a desktop widget, if it is persistent I would like to be able to interact with the object it is referencing at the actual notification, without going to the application layer.

Dashboard Example:  I navigate to Dashboard and I have a notification stating I have an e-mail and I can see the subject of said e-mail.  I press and hold notification and a radial menu pops up with Delete, Reply, Forward for example.  If Gmail account, could have Archive, etc.

I would expect delete to do just that, without having to actually load(from background or otherwise) the e-mail application to delete the e-mail.  If there was another unread e-mail, I would expect that one to now be in its place and be able to interacted with.

Widget Example:  I have a customizable widget that I can Enable/Disable for checking of certain accounts.  If an e-mail comes in, the same behavior in above example would be nice here however if I reply I have the option of doing it within the widget on the desktop.  Same for IMs, text messages.

E-mail contains an attachment? When I am pressing and holding an "Attachment" option comes up that allows me to select Play or Save.  Could have ability to set default locations, etc.

In my mind I am thinking of the Digsby IM Client or Tweetdeck for Twitter interaction, all in-line and instant access without having to open up the corresponding application on the N900.  This could allow for much quicker access and if done right, seamless integration with the device, if possible? :)

Reaching for the stars...