actually i dont think there is alot to think about
n73 is way better in many things
1- bigger and better screen ( 2,4inch compared to 2.0 inch)
2- symbian OS with all the adv. of a smart phone.
3- very good video recorder ( n73 with qvga in mp4 format vs k800 with qcif in 3gp format )
4- 2 speakers with 3d sound
5- almost the same in picture quality but i think k800 is little better
6- supporting more multimedia formats.
7- supporting EDGE + 3G networks
no there is not but it will be. already started showing since the the first 9.1 phone came out .... beside not only the apps ... the performance it self ... for example the call log and saving all these logs.