I have a Blendtec, the one from the commercials. I went through 3 blenders (all of them broke) before settling on the Blendtec and haven't had a single problem in the last year or so I've owned it. My friend has a Vitamix which is pretty much on par with it, as far as power goes. What it really boils down to is, well, just that - the Vitamix can pretty much boil stuff while the Blendtec just gets stuff warm. I'd say the Blendtec is more powerful, but the Vitamix is better at getting soups hot. It's a simple trick; the motor spins for long enough that the base gets hot and heats up the food. The Blendtec can get food warm but not boiling, at least from my experience. That is the one area that the Vitamix is better at.
There are a whole lot of things that I like about the Blendtec. The jar is thick plastic, so it's shatterproof and chip-proof as far as I can tell. It has a square design, which makes it REALLY easy to pour - there's a corner on every side! It has measuring marks on the sides, which is nice when you're making the recipe in the blender itself. It has solid-state buttons on a little membrane pad, so you don't have to worry about mechanical buttons wearing out, getting dirty, falling off, or getting stuck. It's dishwasher-safe, which is nice. The base isn't, of couse, but it's extremely easy to clean since the only "real" button is the power switch. It can really turn a blender full of ice into shaved ice in about 10 seconds - the good kind like you get at snow cone places, not the chunky stuff.
If you're doing semi-liquids, it usually helps to keep things more on the liquid side. For example, if you're making a margarita with ice, you'll want to add more liquid because it will spin so fast that the bottom will freeze up and create a hollow area on the bottom. That's a sign that you need more liquid to keep things moving. You also have to be careful because it's like a food processor on steroids...chopping can turn into pureeing VERY quickly. One day I was feeling lazy and put the ham and cheese for my omelet in the blender with the eggs instead of chopping it by hand...it completely liquified both of the solid ingredients lol. It was way more power than I was used to initially.
It does well with solids, too. You can make peanut butter it it quite easily (it has recipes for different nut butters on the website). I've made regular and honey peanut butter. You can make salsas and marinaras really easily too, no food processor required. It will chew through carrots, tomatos, and garlic like nobody's business. I've made ice cream and cheesecake in mine as well and they both came out excellent. I also make a lot of grilling sauces, like honey mustard sauce for my BBQ chicken.
The only downsides are the price and the noise. It's $400, so unless you have a large kitchen budget or really use your blender on a daily basis, it's not worth it for most people. It's kind of like buying a dump truck to make Home Depot runs - it's ridiculously overkill, but you know you will never,
ever have a problem with it, hehe. I use my blender at least once a day, if not more. Even if I do an omelet, I just toss the eggs in to whip up because cleaning is as simple as a squirt of liquid dish soap, some water, and pressing the blend button for a few seconds and then rinsing out. The other downside is the noise. You almost have to wear earplugs to use it, especially if you put it on a high-speed cycle like Ice Crush.
Overall, I'd recommend the Blendtec to anyone who never wants to have to buy a blender again. It's ridiculously powerful and extremely durable. I love mine. It's one of the few kitchen gadgets I wouldn't ever part with (along with my George Foreman grill). If heating up soups is your thing, then get a Vitamix. It's pretty close in power. However, you can just pour it from the Blendtec into a bowl to microwave or into a pot to boil if you want it really, really hot, so it's not that big of a deal. I personally like the design of the Blendtec better.
Oh, and smoothies are killer