It can be tempting to not use the lid if you’re just doing a quick touch-up or a minor blend job. If you do, realize that you are entering the danger zone. First, if the switch and knob are not on the variable/lowest setting you could send the contents of the pitcher all over the kitchen. Second, if you happen to be tempted to use the tamper when the lid is off, it’s game over. The length of the tamper and the hole in the lid are designed to allow the tamper to reach very near the blades without hitting them. If the lid is off, there’s nothing to stop the tamper.
NEVER USE THE TAMPER WITHOUT THE LID!!! NEVER!!!
If you do, and even if you try to be careful, once the tamper touches the blending mixture, there is quite a bit of suction that can pull it down into the blades (this is how the Vitamix keeps things circulating). The tamper is designed to break before the blender does, so at least you don’t ruin the Vitamix, but the tamper is toast, and whatever you were making is also ruined because it’s full of tiny bits of plastic. I’ve tried to pick them out, but with the Vitamix’s shredding power it’s a lost cause.
I keep this destroyed tamper behind my Vitamix to remind me of the perils of running the machine without the lid.
All that said, this was pure user error. As long as you use the lid there’s no problem. The lid and tamper are a pretty clever design, since the lid lets the tamper get close to the blades without hitting them.*
If it happens to yours, you can easily order a replacement.
Update: There are now three different Vitamix tampers, so make sure you order the right one for your container. If you have the tall/narrow classic 64-oz container that comes with the 5200 and similar models, you want the Classic Tamper. The Classic tamper can be used with the 32 and 48-oz containers because it has a secondary flange. Or you can use the smaller Mini Tamper with the 32 and 48-oz containers. For the short/wide 64-oz G-Series container, and the S-Series 40-oz container, you want the Low-Profile Tamper. The previous links are to Amazon, but you can also order direct from Vitamix.com. (Amazon’s prices fluctuate, so if you want the best price, check both.)
Also, check out this tamper mishap on TV (once it’s playing, note the little minus button in the lower right for slow motion):
*I’ve heard stories of people who managed to blend their tamper while the lid was on by pushing on it too hard. I’ve never seen that happen first-hand, and I imagine that you’d have to push really hard. So don’t push on the tamper with all your weight. You can push on it pretty hard without any problem though.