I bought my SP1 on launch day. The keyboard stopped working 3 days later. MS practically begged me to exchange it and so I started the process since Best Buy didn't have any stock to exchange it. It was supposed to be an advanced exchange but since stock was low even for MS, 2.5 weeks went by and they still hadn't shipped it. I was at Best Buy again and they happened to have some so I did an exchange with them. 2 days later, my replacement from MS showed up so I just returned it to them.
The second time I replaced it was about 7 months later. The fans started making noises. I started a chat session with a surface tech who initiated the advanced replacement. The new unit arrived 2 days later and I did the swap. On both occasions, the replacement units where in perfect, flawless, condition. In each case MS was very friendly and willing to replace the unit. I didn't feel like I had to convince them or anything like that. While I was frustrated to need replacements, I understand that things happen and they did they best they could so I'm happy.