Symbian is probably the best mobile OS out there, capable of running on multiple types of devices with very little hassle and excellent hardware management.

UI though, needs re-work. I am actually not sure that for my particular use cases, Maemo 6 is going to be better than Symbian^4.

In any case, since both Maemo 6 and Symbian^4 devices are supposed to be released this year, a side by side comparison will be interesting.