I use both the crossfading & gap killer on my mostly alternative station and I have to say once you tweak the crossfading module just so it does a very good job roughly 99% of the time (for my tastes and music format). The 1% it poorly crossfades you can set manually in the song's setting tab (X-fade).
One crucial point that will dramatically affect crossfade is the "loudness" of the original mp3 files. It is essential that all your music be set to roughly the same gain even if you're using a DSP compressor/limiter to help level the overall loudness of your station. Think of this as "riding the gain" if you are a dj familiar with running a broadcast board with faders or pots.
I highly, highly recommend the free MP3Gain tool available here:
http://mp3gain.sourceforge.net/ (Set the target volume somewhere around 88-92 db - I use 89.0 dB; and make sure you use the option of "don't clip when using Track Gain" in the options tab. That don't clip is extremely important especially when massaging material that is already highly clipped - e.g. modern pop music.)

As the website says:
Quote:
MP3Gain analyzes and adjusts mp3 files so that they have the same volume.
MP3Gain does not just do peak normalization, as many normalizers do. Instead, it does some statistical analysis to determine how loud the file actually sounds to the human ear.
Also, the changes MP3Gain makes are completely lossless. There is no quality lost in the change because the program adjusts the mp3 file directly, without decoding and re-encoding.
This crucial step in preparing mp3s for broadcast is often overlooked. Your final stage compressor/limiter will do a much better job if the content that hits it is more consistent in the first place.
Standardizing your mp3s will also help the crossfader trigger crossfades at a more pleasing point (generally).
There will always be some songs that you need to set the X-fade point for, especially ones that end with a voice out cold.
There's no one size fits all setting for crossfading, but here's mine:

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Keith (Lumper5) - Deeper Into Music
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