This may be old, but I have tried the Java applet from the "mandarintools" web site to convert from traditional to simplified, and the result is (as far as I can tell) perfect.
The other way round (simplified to traditional) may be a one-to-many mapping, but I'm not interested in that so I have not tried.
In my case, I want:
UTF8 traditional --> UTF8 simplified
Hope it helps