Why do applets that look good under Netscape/Windows look terrible under Netscape/Linux? The layout doesn't work, the text fields are too small to contain the text, etc.
This usually happens with applets that have been carefully laid out to look good in Windows.
For better or worse, the AWT doesn't specify much about what its controls look like - and they can end up varying a lot. The Netscape AWT implements its controls with Windows components in Windows and Motif components in Linux and Unix. If you build layouts tuned to how the controls look on Windows - their size, their fonts, their aspect ratio, etc. - they're virtually guaranteed not to work well with other AWT environments.