Most of the time, that is. Some fonts have a specific clause that they are not allowed to be used on the web, including a surprisingly large portion of otherwise free fonts. The best example of this is the fonts at http://losttype.com/.
Ahh yes, you'd owe Linotype a few hundred bucks if you want to do that. I'd love to see Adrian Frutiger release an open source font before he goes... Imagine if Univers was free!
I'd be okay with a few hundred too. The issue for me is that for web use prices are easily available. For programatic use, it suddenly becomes a conversation about licensing with a salesman, and I don't have time for a long conversation.