The option is not there for all attachment received by non-gmail contacts!
It's new?

I'm still seeing it no matter who sends the document. Are you sure you have Google Docs enabled on the account you're using?

(I know that may seem like a silly question but I first tested it using Google Apps and then realised I haven't got Google Docs enabled...)

may be he's using unsupported formats like docx

Uhmmm...
I've Google Docs enabled, yes, and I can export the attachment from @gmail contacts. But I don't know if is a doc or a docx... the file is an .DOC (wihtout a x), can it be a docx?

I saw this too:
http://groups.google.com/group/Gmail-Help-Reading-Messages-en/browse_thread/thread/fa445dab2164fe46/052cb0d1ac1b4ef2#052cb0d1ac1b4ef2

Same problem with the spreasheets... must be some kind of bug.

would it be a size problem?
they didn't specify any maximal document size.
in my inbox i have a document of 4.7M which have the same problem

500K is the maximal size for uploading it should be the same for importing from gmail.

Bilal, can be this! ;D

The doc has 1,3MB! I'll make some tests!