I use it (right now

) and I am very happy with it. It's extremely fast, surfing with several windows at once is far easier than with IE or Netscape, and the keyboard controls rule.
Of course it does crash sometimes, but unlike IE it doesn't take the system with it and a new 5.0 feature makes recovering form the crash quite easy (it 'remembers' which URLs you surfed on when you crashed).
There are some problems with sites that use code which use MS proprietary code, but for those occasions I still have IE5 installed.