Megan McArdle, in her annual holiday guide to kitchen gadget buying:
If you don’t want quite this much capacity — if you’re cooking for one or two, and hate leftovers — then I recommend getting an older (pre-1990) crockpot off of eBay. In recent years, food safety regulations and fear of liability has caused manufacturers to raise the heat on their slow cookers, which means the food cooks faster. I entertain enough that I reluctantly gave up lower heat for larger capacity (old crockpots tend to come in 2-3 quart sizes, rather than the 5-6 quarts that are standard now.) But only an older crockpot will give you really low and slow cooking.