I just built an HTPC (which is my main PC as well), and I didn't include a BluRay drive. I don't think the cost is worth it yet, and since most things are still on DVDs, there isn't a need to spend more on the drive and on the disc yet.
I will add one later once BluRay is mainstream. IMO, if your PC is not being used as an HTPC (or it is and you don't own many BluRay discs), a BluRay drive is completely unnecessary.
what case did you use for your htpc? As of now the ps3 is sufficient as my PC doesnt have a BD rom. I only have 4 BD movies and it would be useless... also Im sure watching BD movies would eventually take a toll on the GPU... would you know if this is true?