What I relied on heavily with my old setup was asymmetric crossfade. I still use this all the time when playing music out of DJay, by starting the crossfade slider at around 40%, however it's also not completely automatic. I'm still a WinAmp 2 user for my backtracks, with FZLyrics for just that (lyrics), and it features a fade-out which carries over when starting the next song instantly. This is especially important if I decide to change songs half-way through, or if I have to cut a long ending short to keep people on the dance-floor.
I find fade-ins quite useless, but fade-outs essential. Fade-ins mean I miss the count-in on my backtracks, and it doesn't do any good with DJ music either which have signature intros.
In StageTraxx, I've only found symmetrical xfading, so the only way to hear the count-in of my next song is to go with a very short xfade which means I don't really get fade-outs anymore.
Thanxx