First: I think that to purebloods, the only real sin is to be Muggleborn. I know that Bellatrix uses "filthy halfblood" against Harry, but she not only really really REALLY hates Harry, she's also a fanatic who will not even believe that Voldemort isn't pureblooded. Hagrid says that -all- wizards alive today are halfblood or less, and which I imagine this is taking into account lineage over time, I think there are so few Purebloods left (explaining why they're so interbred) that you couldn't possibly make a House out of them. Salazar Slytherin seems to be fine with Halfbloods, if they have the right sort of mind. I imagine that other than in pure snobbishness, most Pureblood wizards (while shuddering to themselves about someone bedding a Muggle) really don't care that much about Halfbloods. So, while I imagine Snape probably wanted to keep his father's identity secret, since his Muggle nature was on file in the library, he was unlikely to have done a great job of it. Luckily, it wasn't something the Gryffindors were likely to insult him with.

Also, I have never seen anything in canon which leads me to believe Snape was unpopular among Slytherins. He was famous throughout the entire school for his brilliance in the Dark Arts, and in Potions- his Head of House's subject. He was one of Slughorn's favorites and hang out in the same group (when he wasn't off being a loner) as Bellatrix Black and the Lestranges.

*grins* Just my two cents, since this is a fun discussion.