Sometimes people might question the tangible value of going to a conference. You're out of the office for a few days, so you lose that work time. You attend a ton of sessions and you're drinking from a fire hose, so after about half a day you feel totally overwhelmed. Does any of it stick?
I can tell you for sure that it does.
The other day someone in my department asked me if there was an easy way to compare two lists and weed out any duplicates between the two. I was quite busy and couldn't remember off the top of my head. I said, "It's been done, so don't write your own. But I can't remember which module it's in right now."
When we had YAPC here in Buffalo, just about our entire staff attended. We do a lot of Perl development and YAPC is so affordable, there was no reason not to. So I was very happy when she came back a few hours later and said, with a big smile, "List::Compare!"
Now you could say I should have remembered that, and you'd be right. But in this case I didn't and attending that session two summers ago saved her from spending time searching. And it definitely saved her from the even worse fate of writing her own comparison code.
It's hard to put a dollar figure on what might have been, but there's no question in my mind that just remembering that one session more than paid for the price of attending YAPC.