Welcome Screen: All you need to do is input your email address and password. Nokia Messaging takes care of the rest. It managed to set up my Gmail and Ovi inbox without any problems.
Inbox: Below is a preview of how my inbox looks. You can see the Gmail logo in the top left. If you have other accounts set up like Yahoo, Ovi, etc. you just click that icon and it will list your other inboxes. Tap the Inbox icon in the top row and it will show you the other folders like Trash, Sent, and your IMAP folders. Tap the Date icon and you can also sort by Subject, Sender, Flag, Priority, Unread, and Attachments. At the bottom you can reply/forward, delete, and compose. To scroll through the list you can either drag the bar on the right side or put your finger anywhere on the message list and move it up and down. I prefer the second method as it works very well.
Message: Here is what it looks like when you view a specific message. In the row of buttons on the bottom you can choose to reply/forward, delete, and flag your message. In the options menu you can mark unread, move, select text, call sender, and compose.

Compose: This is where you compose or reply to a message. The icons at the right allow you to send, attach, and add priority to your message. unfortunately I couldn’t get a screenshot of this in portrait view, the screenshot app will not let me. So here it is in landscape…
Landscape Mode: As you see above Nokia Messaging also works great in landscape mode.
Extra Notes:
There are a few other notes that I’d like to mention before wrapping up this post. There is a Touch And Hold gesture that works when you highlight an email and hold your finger on the screen. A menu comes up with the following actions: Delete, Reply, Reply All, Forward, Mark Unread, Flag, and Move. Unfortunately I wasn’t able to get a screenshot of this because the screenshot application won’t capture it. This feature needs a little more work since it sometimes doesn’t bring up this shortcut menu, instead it thinks my finger is trying to scroll. This actually happens across the board. Sometimes when trying to open a specific message by tapping it, the application thinks I’m scrolling and just moves the inbox up and down. I’m sure this will be worked out when the first beta version is released, keep in mind my version is still alpha.
Before you ask - HTML is still not implemented in this version. I can assure you that the developers are working around the clock to bring this functionality. UI design is also being polished, and home screen integration is on the to-do list.
Slightly Off Topic: For all other version of Nokia Messaging: HTML support is “coming soon”. I’ll let you know a soon as it’s available.
If you have any questions about Nokia Messaging for the 5800 feel free to ask! If you haven't tried out Nokia Messaging and you have a device other than the 5800 get it from http://email.nokia.com