But BOILING implies that there is a LOT of liquid at boiling temperature, no? And generally that's not what you're doing in the slow cooker at all.
You want very little liquid going in, because many, if not most, ingredients release liquid as they cook, and that is partly what gives you the excellent flavour and makes the sauce. And the temperature is usually much lower, so not enough to get a boil going.
Really though, if you've had a slow cooker and found everything was disgusting and watery etc etc etc then it is most likely that YOU were doing something WRONG. Now, it may just be that you can't or won't adapt to a slightly different way of cooking - fine, then clearly a slow cooker is not for you - but it's really not the fault of the slow cooker.
As doadeer so excellently puts it:
"If you think how many cultures have a famous food that is a slow cooked meat for hours and hours - belly pork, gammon joint, beef bourginon, beef stifado - the idea of cooking meat long and slow over heat inside liquid is everywhere. A slow cooker just allows you to do that without leaving your hob or oven all day."
We are not vegetarian but eat very little meat, and I use the slow cooker loads. I've actually found it really good with vegetables - I'd heard tales of tasteless mush but haven't found that to be the case at all. Ratatouille made in there is simply one of the most exquisite things to come home to, the house smells divine. And obviously any type of curry is great, anything with pulses, I did a split pea soup in it the other day (literally just threw in dried peas, stock, seasoning) served with a homemade sourdough bread, was fabulous.
Oh and of course slow cooker rice pudding is HEAVEN.