I applied to Twitter and the HR person asked me for dates for phone interviews, and then didn't respond for weeks after I gave them the dates. Twitter HR and their recruitment process is amongst the worst I've ever encountered.

Also, if you get rejected by them, they don't have the common courtesy to let you know, even if you try contacting them. Apparently it's beneath them to respond with even 140 characters.

I applied for an internship and got two interviews, but they seemed pretty disorganized. They often called at different times from what they said they would (usually when I was in class). They also had to reschedule the interviews several times. The initial informational phone call I also got twice which was strange (about half way through the second one I mentioned she had called the day before with the same information). Seems like a fun place to work though and the interviewers were great.