Everyone seems to be afraid of spiders. It's not often that someone is quick to hold a spider in their hand or pet it. People have a near-universal reaction to spiders that could be described as unwelcoming. Considering how common the human fear of spiders is, it's helpful to know what spiders are worth being afraid of and which spiders you can simply walk by without a care in the world.
Hint: the number of relatively harmless spiders is almost equal to the number of all spiders.
While some people can be allergic to the bite of the wolf spider, people can also be allergic to pollen, which is much more common in certain seasons than wolf spiders. Barring serious allergic reactions, widow spiders and recluse spiders are likely the only kinds of North American spiders posing a serious threat to human bite victims.
Wired has an enlightening article discussing their relative lack of danger. While a bite from the brown recluse can cause necrosis, it often doesn't. Furthermore, brown recluse spiders can't bite through socks, pajamas, or any other clothing. In fact they can only bite through skin that is particularly thin. Also, they're called "recluses" because they tend to be, well, reclusive. Imagine that.
While they do prefer indoors to outdoors, they also prefer places unpopulated by humans to places where humans are constantly gathering. Most times, brown recluses only bite when they fear they're about to be crushed, and even then not all their bites result in necrosis.
However, approximately three out of five black widow bites produce something called a "dry bite." This is a skin puncture via the spider's fangs, but resulting in no venom being injected into the human. It may hurt a little, but a dry bite results in little more than temporary, localized pain. You can, of course, still crush the offender in pursuit of revenge. This is a personal decision.
That said, an other-than-dry bite from a black widow is likely to ruin your plans for the next week or so, or if left untreated, it could ruin plans for the foreseeable future.