5 Brand Sluts: Yeah, we're talkin' to you. Trendster and JWT Exec VP Marian Salzman defines "brand sluts" as consumers who flit from one brand to the next with no sense of fidelity to any of them. While the connotation is negative, brand sluts are in fact savvy consumers.
—Rich Thomaselli, "Trends to watch in 2007," Advertising Age, December 18, 2006

From this consumerism emerged a new retail animal in the '80s and '90s: the logo queen. She was obsessed only with polo ponies and interlocked C's. She was loyal to her logos.

Today, that creature has morphed into something that goes by the unflattering name "brand slut" (the nicer term is "brand promiscuous"). She would be the fashion and beauty consumer who flits from one brand to the next.
—Greg Morago, "The brand sluts," Hartford Courant, January 1, 2007

According to market research, at a certain age — they peg it, I think, at 35 — a person just suddenly knows who he is. What he likes to eat. Which beer he prefers to drink. What car he wants to drive, which paste he wants to brush his teeth with, and how he wants his underarms to smell. So after about 35, the average consumer is unreachable. No matter how much money a company spends trying to convince him to smell spicier or sexier, he's unlikely to change.

But the 18 to 34 crowd, apparently, are disloyal brand sluts. They hop and whore around the place, trying this new beer or that new car or body sprays and tooth whiteners: they can be bought, in other words. And that makes them desirable.
—Rob Long, "So 40 is the new 30, I say to the network executive. No, he explains, 40 is 30 with money," The Sunday Telegraph, November 20, 2005

The brand slut is also known as a label whore or, as I most often use it, the corporate whore. It tends to depend on the person in question:

A Brand Slut is into products by a certain company or set of companies. Most commonly technological - the "iSlut" is rapidly emerging as a name for those who buy everything Apple produces.

A Label Whore is usually particularly designated for people who buy massive amounts of designer clothes - and usually based on whichever label is en vogue at that time.

A Corporate Whore is someone who commonly will pass over a superior product by a small company and automatically buys the equivalent product by the biggest company. Examples include people who will automatically buy an iPod when looking for an MP3 player, will buy McDonald's over local take-away food or will only watch mainstream films, rather than independent efforts.