When should I start to be concerned?

Accounting Chick

I know that it's very common for breastfed babies to go longer between poops.  I understand that it's because babies systems are able to utilize everything in the BM, so there is often little to no waste left over.  However, my LO has not had a poop since Monday (7 days now).  At what point should I start to get concerned and attempt to induce a bowel movement (via such methods as taking his temperature rectally, etc.)