Perhaps the most dramatic example of variation in olfactory abilities in humans is anosmia, or the inability to smell. However, this isn't always due to broken olfactory receptors -- some total anosmias are due to cilia (small hairs) that don't function properly. (This paper mentions that.)
Specific anosmias, or insensitivities to particular smells, are probably closer to what you're asking about. The textbook chapter I linked to below talks about how proportions of the population lack the ability to smell certain odorants -- for example, about 1/10 people cannot detect ethyl mercaptan, which is the scent given to natural gas leaks. These specific anosmias are generally restricted to just one odorant (smell), which suggests that it is likely a receptor deficit. (EDIT: The comments below have even more examples of scents that vary from person to person.)
Interestingly, many conditions are associated with a decline in smelling ability and range, like Alzheimers, diabetes, and taking certain medications. These declines can be because of fewer olfactory receptors or because of deficits further along in sensory processing.
I couldn't find any papers assessing smell variation across all humans -- doctors rarely think to assess smell, so there isn't much data on "normal" populations. Also, it doesn't seem like the genes controlling olfactory receptors in humans have been characterized well, so it would be extremely difficult to do a comparison on the genotypic level.
In sum, there are definitely differences in the ability to smell a wide range of scents. To my knowledge, this hasn't been characterized in an especially systematic way. (If it has, I hope somebody on here knows otherwise!)
This chapter of Purves' Neuroscience gives a basic run-down of olfaction and some possible variations in it.