Yup, I got tired of coming up with cute titles for these. Blame the children... they have been throwing up on me all weekend, and I am exhausted!
Alpaca is currently a very popular fiber. This is understandable, as alpaca is (generally speaking) delightful to work with. It is soft and smooth. If you like natural colors, alpaca can be your friend, as the beasties come in about fifteen kajillion different colors.
The downside of alpaca is it has absolutely no memory. Seriously, look at South American fashions from back in the day... see any ribbing? Cables? Nope, not a chance. Ribbing done in alpaca just sort of sags out of shape, and doesn't do any of the things ribbing is supposed to do, except maybe look cute. Even for lace, many knitters complain that 100% alpaca is too saggy to properly show the pattern. Of course, this isn't necessarily a BAD thing... you just have to figure out how to use it. One of the easiest ways is to just mix your alpaca with a nice, springy wool, like merino. That makes you loose some of the unique alpaca qualities though. My advice is simply to choose your patterns very carefully. Crochet edgings can lend your work support. Make something that's supposed to be soft and drapey, and it will work just fine!
The other big deal with alpaca is that it is supposedly hypoallergenic. This is true, but not the way most people think it is. Hypoallergenic simply means that something is less likely to cause an allergic reaction than similar substances, not that it's impossible to be allergic to it. Believe me, you can be allergic to alpaca! It is simply less common than wool allergies. In addition, alpaca contains no lanolin, which eliminates lanolin allergies entirely. So if you're allergic to wool, it is certainly worth a try. But don't pin all your hopes and dreams on it.