How common is it for somebody to have problems from spider bites?

Not common...: ...But, there are some dangerous spiders out there. In north america the more common are the black widow (pretty immediately painful bite) and the brown recluse (causes delayed local tissue destruction). These bites are relatively rare. Most "spider bites" can be treated with ice, rest, tylenol, (acetaminophen) and time. Sometimes an anti-histamine or topical steroid can also be helpful for symptoms.