Today, I received a call from a friend asking me if I got the e-mail she had wrote a half an hour earlier to my Gmail account. I said no, and assumed that she had sent it to a wrong address.
However, 3-4 hours later, I received the mail we were talking about and became suspicious after remembering some other similar incidents in which I had suspected delivery delays from Gmail. I made a quick search and found out that this is a 'hot' subject recently, both in blogs and discussion groups. For example this Gizmodo post from Feb 2008 or this recent article, raise the exact same question and the users ' feedback indicates that there is actually a Gmail delivery problem.
I only hope that it is Google to blame and not anybody else..(who said NSA?)