Not ever! Blu-ray is heavily DRM encumbered, and every purchase of a drive and/or disc puts $$ in Sony's pocket, who I will NEVER again support! Stick with DVD's. Yes, BR can provide higher resolution, but not enough to justify Sony's egregios anti-consumer behavior! 720p (DVD quality) is pretty darned good, even on HD TVs. So, just say NO!
My reason for this? Some years ago Sony delivered CD albums infected with a rootkit that bricked and/or infected millions of computers. Did they every pay compensation for this? No. Did they ever apologize? No. As far as I'm concerned, hacking Sony is a public service... :-(