At least custom games are now largely bullet proof from what I'm seeing and chatting with other people (except, obviously for people who can't connect to anyone).
Hell no they aren't. Here is a list of things I have noticed that still break custom games:
1. 5v5 - For some reason, it seems to work fine up to 4v4, but as soon as you try to add those 2 more players, all kinds of wierd things start happening.
2. If players quickly join and then leave again, or join and then leave before they are finished connecting to everyone. This can result in them getting stuck in the "connecting" list even if they aren't in the game any more.
3. Seems like people aren't always updating their lists of players to connect to. Sometimes a player will leave the game (as in scenario #2) and ALMOST everyone will disconnect from them, but one person will be stuck in "Waiting to connect to <leaver>" state, and they never get the memo that that person is no longer in the game. Even worse is when they are stuck in the "Attempting to connect to <leaver>" state because then they never try to connect to anyone else, and I have to kick them.
4. Many people connecting at once. This is a nightmare - everyone is simultaneously connected to some, waiting to connect to some, and attempting to connect to some. Sometimes this settles out; usually it results in one or two players being "stuck" in some way and unable to connect to each other. This usually results in one or two players leaving before they are finished connecting, and then the people that are actually IN the game experience #2 above.
The only reliable way to get a big game going is to keep slots closed and let players in 1 or 2 at a time; that way, if a player causes an issue, you can tell who it is and kick them before they screw everyone else's connection dialog up. However, this takes FOREVER and, given the A.D.D. attention spans of your average gamer, means that people in-game often get bored and go elsewhere before it fills up.
edit: Oh and there is a new kind of bug today. Happened to me AND another guy who was trying to host before me. Fatal error when trying to kick people from the lobby. No I don't have the log files. Sorry.