If you choose to obfuscate your midlet, you gain two things: the final size will be reduced, and the contents will be hard to disassemble.
But. If you turn on obfuscation in NetBeans, it will be used for your local debug builds as well. Due to that, you will lose debugging information, notably filenames and line numbers in stack traces.
two: Version strings must be handled with care.
My phone (SE K610i) refused to install a midlet with version "0.2.991", or anything longer than 6 characters. A different phone (Siemens CX65) installed a midlet with version "0.2.99sync1", which then mysteriously crashed with a NullPointerException that wasn't there with version "0.2.99".
This is bad magic. If anyone can explain it, please do.
three: From what i gathered, there is no way to list files contained in a JAR at runtime.
If you want to do that, create a text index at compile time and include it in a known location.
and four: Some older phones, even though MIDP 2.0, don't call Canvas.sizeChanged event.
Or maybe they do, but not (citing the spec) "at least once before the
Displayableis shown for the first time." [here] Or maybe they even do that, but don't specify the proper size.
So don't rely on it.