Really? Hmm. It has been 5+ years for me, my bad. But what's the point of the ddos's then? I see netflow graphs of huge attacks on major efnet servers on a regular basis.
Not too long ago there was an ircd exploit that killed servers and split 100% of efnet, which had never happened before. Not to mention its down 50% of its user base from a few years ago. Tough times for efnet.
All servers on the largest IRC networks are very well connected to the internet and servers that are not, wont be able to last long on these networks.
Some IRC servers wont allow you to create new IRC channels during a network split, so an attack where the network is being split constantly can cause quite a lot of annoyance for the rest of the users.