I love the service so don't think otherwise with me complaining about two things recently.
I would understand this if they did it against viruses, but then shouldn't they just block executable files?
The error message:
<...@gmail.com>: host gsmtp171.google.com[188.8.131.52] said: 552
5.7.0 Illegal Attachment
So now I'm only attaching 7-zip archives.
Update: In other Gmail-related news, I just saw a page about operators you can use in both filters and mail searches that I hadn't seen before. Very nice. I only knew about from:, to: and OR before.