My goal with my son was 2 years. He ended up nursing until right around his third birthday.
I am very, very glad that he nursed through toddlerhood. He was (and still is) a VERY picky eater. He ate very little in the way of solids until he was close to 2, but I never had to worry, because I always knew that he had the breastmilk "insurance policy." He was also extremely healthy, and still is. He very rarely gets colds, and he has only been throwing-up sick twice in his life (he's 5 now). Before he stopped breastfeeding, he had only had 2 colds in his life and he had NEVER thrown up, other than being car sick.
It was also great for me, for selfish reasons! It was nice to have a great rack for such a long period of time, and when my son was between about 6 months to 2 years old, I was the thinnest I've ever been while eating as much and anything that I wanted.
When they get older, breastfeeding becomes much less demanding as well. After the age of 2, my son only nursed 2 or 3 times a day, and it was easy to leave him overnight. We didn't really nurse in public after about age 2 either, so if that makes you uncomfortable, it's easy to avoid. As they get older it's easier to set limits and make the breastfeeding relationship something that's comfortable and happy for both of you.
I say just go for it, and don't set a limit for how long you're going to nurse. Personally, my hope for every baby is that they can get at least a year's worth of breast milk. So I'm super happy if anyone tells me that is their goal. But I think a lot of women underestimate the benefits of nursing longer than that.
ETA: A lot of women are totally freaked out at the possibility of biting, but I found that it was a very short phase and it was really no big deal. Around 8 months, he caught me off guard a few times causing a gasp and an "ouch," but it didn't really hurt that much. Most of the time I could anticipate when a bite was coming and could slide my finger in. Definitely nothing to get one's panties in a twist over. :)