Miro:
I don't like to jump on any bandwagon, but would agree with Ginger's ascertain that it depends.
My personal experiences are also similar to Ginger's regarding loyalty to my automobile brand. I like GM, specifically the Pontiac brand, for several reasons but stem from a long family history of loyalty. I'm now driving my second and consecutive Grand Prix GT and have owned/leased several Pontiacs over the years. Unlike Ginger's bad experience with Ford dealership service, I have no complaints about my local Pontiac dealer. I realize I pay a premium for oil changes and other maintenance service outside of warranty, but since I lease my car, I feel better about maintaining a service history at the dealer, in the event there's ever a dispute (yes, I was burned about 20 years ago) when I return the vehicle at close of lease. In addition, I'm always treated well by my service advisor. So, there you have it!
I would also suggest that there are many factors and variables (too many to list) at play that span a consumer's attitudinal and behavioural drivers that affect brand loyalty. Personally, I have an aversion to shopping (like most typical guys), so when faced with having to run shopping errands, I seek the most convenient shopping option and experience within proximity to my home. The fact that I'm also time starved, is a factor at play.
Within 5 km of my home are at least 6 grocery stores - some premium, some discount, some big box, some in between. Even though there's a Loblaws grocery store that I prefer to shop at because from my perspective, it has a better selection (breadth & depth), consistent quality (meat, fruit, vegetables), wide clean ailes, stocked shelves, I often avoid it due to congested parking and long wait time checking out. So, I go to Sobey's that's somewhat comparable, has easier access to parking and is not as busy hence shorter check-outs, but lacks some of the premium store's primary and attractive attributes. The conscience compromise I make is driven by the value of my time and ease of convenience.
I also purchase my gasoline at a local Shell station because it's right around the corner from my house; again, based on time and convenience, even though there are several other gas stations in my local neighbourhood that might have lower prices, but requires a bit more time and effort to reach them.
In closing, looking at my consumer profile, one might conclude that I'm a monogamous based on the examples I cited above, which are some but necessarily totally representative of my entire brand purchase behaviour and preferences.
Hope this helps the discussion!
Phil