Bím ag rith vs Rithim
A few people have been confused by structures such as this, so I thought I'd clear it up:
Táim ag rith = I am running
Rithim = I run
Bím ag rith => This is a bit odd on its own, so I'll put it in a more natural context:
Let's say in response to "Every morning when you see this man, what are you doing?"
Bím ag rith nuair a chím é = I am running when I see him
Bím ag rith = I am running
(Chím is a dialectal form for "I see")
So you can see it is habitual (something you do repeatedly) but progressive (when you see him you are "running", i.e. the action is still progressing/occuring).