yes, unlike using something like Traktor, with Live you definitely have to test and demo things before you take your set out into the real world. with true DJ applications you can always make adjustments of pitch and push forward to conpensate and avoid train wrecks, but not with Live. You have to absolutely test every single clip you plan on playing (or not) live.
a good tip, if you can, is to always warp and practice with an external harware drum machine synced to Live as a slave. i've been testing and warping a bunch of tracks and i've been playing along a simple drum loop on my Machinedrum very successfully. you can also make a simple MIDI clip playing a beat through Impulse. this tip in combination with this tutorial
http://www.ableton.com/pages/tips/2004_04 is a perfect.