The N9 is for you if you like to use your knowlege of GNU/Linux on your pone. SSH into your phone, edit files directly on the phone's file system, tinker with settings etc. - No way to do this on a 808.

Also, the UI is smoother on the N9 and simpler. (Simple also meaning: less possibilities.) It's just more of a simple every day phone if your use case is making phone calls, checking mails and following your friends on twitter. (The event feed is nice.)

On the 808, you have a number of additional technical goodies that the N9 cannot offer. The usefulness largely depends on your other technical equipment, of course... You have a removeable SD card, FM transmitter, USB on the go to attach USB-sticks or external hard disks, standard compliant 3G video calls, HDMI out, SyncML built in...

I also found the 808 to be more reliable when it comes to 3G data connections. The N9 keeps dropping connections when I move (like in a car or bus), the 808 doesn't.

On the UI side, I found the 808 to be strangely slow, given that it has a faster CPU than the N8. I don't know where all this additional speed goes to, but you hardly ever notice it when using the device.

OTOH, the usual desktop-concept with all the useful widgets and shortcuts is a huge plus for me on the 808. I really miss those on my N9.

I'm not the person to judge the number of 3rd party applications. The few I use are available on both devices somehow. The only thing that my Symbian device has and the N9 doesn't is this whole Microsoft integration with not only Exchange, but also Lync, Sharepoint etc. - I wouldn't use those normally, but a have to at the office, so this is the only software I really need that the N9 cannot offer.

Given all of the above, I have to contradict Kangal; I'd say that the 808 is the better smartphone because it just offers more of everything. The N9 is the cooler device. It doesn't offer anything that the 808 doesn't have. But the things it does it does in a more friendly and beautiful way, if this is of any importance to you.