I can only answer from my own perspective so take it for what it's worth ... not much.

Porn, in my opinion, is about fantasy. So fake is good in that case. I don't expect reality in porn. So in porn, girls with big fake boobies are awesome.

In real life though, big fake boobs look horrible. No more fantasy so when I see a woman with major implants it actually turns my stomach a little. I'm more interested in a woman's mind than her chest and big implants send up red flags.

In summation:
Fake World + Fake Boobs = Good
Real World + Fake Boobs = Gross