I own a N800 (and 770 and N95 and other S60 Phones).
I like S60 a lot, and I love maemo.

I have just ordered a 5800. I think it will replace my N800 and N95 for the time being.
I think it is very strange to compare the 5800 with a N800 (or N810).
The hardware of the N800 is 2 years older! That is long time in smartphone land.

One of the things I like about the 5800 is that it has TV-out and that it has a HSPDA modem build-in (I hope it is just as good as the N95, that device has MUCH better reception when compared to the iPhone 3G).
Also the Flash video support on the 5800 seems to be a bit smoother when compared to the N800.

On the internet is some talk that the 5800 also supports DVB-H with a SU-33W bluetooth receiver.
If it does, than the device comes very close to my ideal device:
-high res touch screen (that was the best part of the 770 and N800 imho )
-good web browser
-wifi support
-HSPDA
-TV-out
-DVB-T or DVB-H receiver

The GPS is also welcome, but for me not that big of a deal (that is why I didn't upgrade to the N810: not a big enough improvement, besides people said the GPS on the N810 didn't seem to function that well).

Also the 5800 is very affordable here in Holland: less than 250,- euros in total (and that includes a year contract with my telephone provider)

Symbian and S60 are very different from Maemo. S60 is a phone OS that is evolving to a mobile computing platform, and Maemo is a full desktop linux environment that is evolving to the same thing.

I hope the new internet tablet will become even better, but for now, the 5800 will do for me.