Qlab will of course always hold a special place in my heart. It was the first Show Control system I've used and so far, the once I've most consistently used. That's likely to change now that I've been introduced to Isadora and managed to program my own show using the program. That being said, Qlab certainly has its downfalls and after some particularly glaring problems using it for Donogoo, I've come up with some basic problem solvers for problems you're likely to run into.
TURN OFF ANY EFFECTS
For the Record, we were running this show using 3 projectors out of a Matrox Triplehead, coming from a 3ish year old Macbook Pro with almost full memory and a solid state drive with 8gb of ram. Our content was plenty condensed but due to the nature of the show (trying to get the lights not to muddle the projections) we began using the Exposure control on the new (to Qlab 3) effects tab. It took about 4 crashes during crossfades and numerous random stutters during animations before we finally realized that it was being caused by the computer trying to load every frame as a different Exposure while also changing the opacity for cross fading. We finally just threw everything into Mpeg Streamclip or Photoshop and turned off our effects however....
AVOID CROSS FADING
Originally our crossfades were meant as a place-holder for some "wild wacky transitions", however as our deadline drew nearer this was pretty much abandoned. Unfortunately the crossfades kept stuttering due to the above-mentioned problem. Should the effects be absolutely necessary I'd recommend fading the next video in, on top of the previous video (keep your layers in mind) and then STOPing the video underneath once the fade up has been complete. This will put much less strain on your system.
USING THE MATROX TRIPLEHEAD
A little something I discovered that I'm sure many people have found before me, but if your using the TripleHead DONT USE ITS SOFTWARE. Just plug it in and check that its recognizing your projectors as one long chain of images. Then in Qlab make a new surface, go to the left and select Underneath Screens assigned the Partial screens tab. There you can select which projector you'll be using and get an automatically sized screen. This should save you a ton of hassle.
I'm sure QLab will continue to grow and hopefully add a ^$#@ing chroma key Effect but until then it's an excellent tool for simple shows and a great place to start to learn show control.