Depends on your line of business and, like any other place, the personalties of the people in it.
Dress is business casual (Florida-style, which is going to seem downright casual if you're from the Northeast), but if you work on sets or in fulfillment, of course you're going to wear jeans and t-shirts.
The creative departments are also pretty casual, with a catch. In marketing, for casual, the more trend-aware your sense of style, the more casual you can dress, if that makes any sense.
The atmosphere is progressive-conservative.
HSN offers organic options in its cafeteria, has pet health insurance for your four-legged kids and is openly gay/alternative lifestyle friendy (and recognizes domestic partnerships when it counts, like in a benefits package), but the company is still pretty square and middle America in spirit.
With its new leadership, this square image is one it has aggressively begun - and needs - to shake to survive in the slick and fast world of multimedia. So far, results are mixed and the mood is tumultuous.