I opened my first credit card when I started university (you know those people with the clipboards hanging out in the hallways, trying to entice you to sign up with free stuff). My limit at the time was $500. Over time they kept automatically increasing the limits, so now I've got two cards each with well over $20K limits. I keep thinking I should call and bring it back down to something more reasonable, like maybe $10,000, but I haven't bothered.
Agreed that credit cards can be indispensable (online shopping with purchase protection, for example, or for shopping in foreign currencies) and the credit rating that you build up is mandatory if you want to do bigger things in the future like qualify for a mortgage or car loan.
Like any tool, however, it can be abused, and it's far too easy and tempting to overspend and carry a balance that takes you years to pay off. Of course this is totally in the credit card company's favour, since they're charging you up to 30% interest, so they're part of the gang of people saying "spend! spend!" Every single month my credit card bill is accompanied by a set of three "checks" that they keep encouraging me to use to buy myself something nice. Every single month I rip them up. The only person who can control your spending is you, so be careful how you use it!