I used the Symbian^3 on C6-01. Since I previously used S40 on E65, the user interface was ok for me to navigate. Actually, I always liked Nokia's earlier interface which was simple and user-friendly (compared with Sony Ericsson/Motorola). They really excelled that time.

Back to Symbian^3, the C6-01 was a bit sluggish with occassional hangs when browsing. Other than that, it was ok. Personally, I would not mind migrating to E7 (Symbian^3) if and when my N900 fails - could get 3G video call and voice navigation.