As far as launch days go, the servers were up a bit over 2 hours early, and were shaky for the first hour of that, many disconnects, etc, as they got more of their hardware up and going. As far as stability goes, once we hit that midnight PST mark, it was pretty fair. On the first daytime, I have not been disconnected at all and no noticeable server lag.
The invite issue for the guild appears to be partly a UI issue, as the invite goes out, it just doesn't always appear on the invited person's list (at least it didn't for mine until I logged all the way out and restarted). Once in, though, you only need that one guild invite for any of your characters.
I've been put into overflow several times, but as a solo player today, it hasn't been a big deal for me. It's Atlas Park 4 all over again. No biggie.
I haven't run into any bugs, impossible material nodes, points of interest or anything. There are a couple of zone events that I've seen several times (which makes them less interesting than I was hoping for this game, honestly), but others have chained into even more events, and each one earns a little something.
The mail doesn't work for me, at all. That makes me sad. That'd really be the only big thing I am unimpressed by. As far as launches go, it's not a bad one at all.
I haven't done much but play through the starter instance for each race and worked a charr guardian to 11, with a little weapon and armorsmithing going on. (I still need to find water to play in to open up those skills for the trident and spear I have).