You can post runs to Facebook direct from your log book.
If you go into your log book, then click "view" from the right hand side near where it says "edit"
Then when the next page opens click "LINK TO THIS ENTRY" from the left hand side. (a box will come up asking if you really wanna do this, click "OK")
Then click LINK TO THIS ENTRY again, then copy the displayed link into your facebook status.
All sounds a bit of hassle but really is simple to do when you get the hang of it.
I dont use twitter so not sure if this method would work as a tweet or not

May I also use this opportunity to invite you guys (and anybody else) to join GRG facebook group... https://www.facebook.com/groups/156615734390640/ ...the friendliest running club in the world !!!!