I'm not sure how it would necessarily be a source of attachment, but I can certainly see that it could be a distraction. After all, what could a diary be other than dwelling in the past or beckoning the future?
Keeping a diary

I don't bother keeping a diary, if it is worth remembering it should be automatically remembered. Needless to say I don't remember much .

http://groups.yahoo.com/group/Buddhist_Sutras/
I try to post a short quote of a certain buddha each day. It's helpful and generates great merit.
Do you think it is okay to keep a diary, or will it lead to more attachment?