I like symbian devices, particularly Nokias. They make some of the nicest handsets around. I love my 5800, and S60 v5. I liked my previous S60s phones and my Psion EPOC devices before those.
That said, I hate the development environment, it is absolutely and consistently dreadful. It's a wonder anyone develops for this platform. The Wiki is full of out-of-date examples, and contradictory advice. The compilers are terrible - two completely different free compilers used for the emulator and phone (with different bugs), or a third commercial one which can actually generate decent ARM code - all WIN32 only, of course.
The Symbian C++ API is just awful. OpenC made it bearable, python makes it usable. Nokia's focus is, however (like an ADHD sufferer) shifting once again - this time to Qt. They are currently shipping a 5-600MB Qt SDK for Linux, which can *only* produce code for an emulator!