One thing that you will not get out of most Blu-ray players that you will out of an actual computer is a browser. Some devices are starting to incorporate a browser though.
I'll be honest, I used to (and technically still do) have one of my computers connected to my TV and customized with an IR receiver and all that fun stuff. However I never use it. I almost always use my XBox 360 or PS3.
But as mentioned, there are tons of options out there (Roku, Boxee, etc).