For my part, I always like to start with the bad news and wash it down with the good. The worst launch day offender in my book was SOE's Star Wars Galaxies. June 26, 2003: a date that will live in infamy....ok maybe it wasn't that dire, but I distinctly remember taking the day off from work, purchasing the retail client at nine in the morning, and finally making it to character creation and the dust-caked streets of Mos Espa around eleven that night. In between, there was much swearing and spamming of the account login launcher, and even more Starsider server lag when I finally managed to jack in.
On a more positive note, recent MMORPG releases seem to be improving in terms of both stability and performance. My opening day experiences with both Lord of the Rings Online and Warhammer Online were completely free of login and stability issues. What about you, dear readers? Care to share your launch day horror stories or happy endings?