Dota2 is Valve's first multiplayer game where they run all the servers themselves. It's also their most popular game (by a factor of 10x) [0]. Scaling to that number of players takes a lot of work, and from what I've seen (comments from Valve devs), their devops team is only 2 people [1].
The current server instability has to do with a large patch (550MB) sent out yesterday that added a new game mode that is actually an addon[2]. This addon system looks fairly new and may be taking its toll on the servers.
The last 4 major updates to DOTA 2, have been unplayable for about 2-5 days. They did an update earlier today, my friend in Australia hasn't played all day because servers are down. I can't play in Singapore at 2-10am, servers are still down...
Unfortunately, he's right. I applaud Valve's focus to Linux, but DOTA Linux has had major bugs for months now (the most severe of which is the game taking 1-2 minutes to load and timing out, whereas Windows on the same machine loads in a few seconds). They don't seem to really want to fix the errors, as all my friends are having the same problem, so it's not exactly hard to reproduce.
