Check
http://netsplit.de/networks/ and you'll see that IRC is as strong as ever. Where a few years ago there were 'the big four' networks with most of the users and then many other networks with very tiny amounts, these days there are a different big four, and several medium sized networks in the tens of thousands of users range. There are more users on IRC now than ever, they're just distributed a little better. The reasons for this, and for DALnet taking such huge user hits is that DALnet was attacked continuously for months, meaning most of it's users had to find other networks to get their IRC fix. Even after the attacks stopped, DALnet changed it's Acceptable Use Policy to ban filesharing channels, so much of it's old userbase hasn't come back.
