Yes it is. I am not a into it as a business, but last year, i managed to secure 3 expired domain names. I checked the domain’s attributes on Spamzilla, and they sounded nice to me, i just had to catch them. I did set them for sale on GoDaddy auction. And believe me, i sold one of the for 500 times the amount i bought it for. Since i had just hand registered it.
That shows that those who have invested heavily in domain flipping must be making a kill everyday. Because there is no standard price for domain names, the owner can set any price s/he wants.