I don't know if it is actually due to throttling or not, but Netflix is preceived at least to still be throttling me.
This score is based on a number of factors, with the objective being to maximize subscriber happiness (one example question is whether is it more valuable to have quick turnaround for a frequent subscriber who is already happy with the service, versus an infrequent user who might be on the fence--it is not obvious who would be more sensitive to and negatively impacted by a delay in receiving the next DVD).
(Source: I work with people who previously worked at Netflix. This is not confirmed fact but a loose understanding based on casual conversations.)
DVD Terms and Conditions
As a result of your viewing habits and our operational practices, the actual number of DVDs you rent in any month may vary, and you may experience differentiated service during the course of your membership. Also, such service may be different from the service we provide to other members on the same membership plan. The type of differentiated service you may experience includes, (i) the shipment of your next available DVD occurring at least one business day following return of your previously viewed DVD, (ii) delivery taking longer, as the shipments may not be sent from your local distribution center and (iii) the DVDs you receive coming from lower in your Queue more often than our other members.
Edit: Klinky cited something, instead of vaguely referencing years-old events: http://news.ycombinator.com/item?id=2757009
This sounds less like "throttling" (i.e. you've gone through too many discs this month) and more like balancing (i.e. how do we distribute 100 copies of this movie to the 1,000 subscribers who have it at the top of their queue).
You are correct that it really only affects situations where demand outstrips available supply.
While I believe internally Netflix called it smoothing or something like that, throttling isn't an inaccurate term either.
Much of the anger came from the fact that an existing customer could put something in their queue & see "Long Wait" which may mean that movie would probably be delayed weeks or even months. Meanwhile their friend might setup a new account that weekend & get that same movie immediately. This lead to people feeling as though Netflix was shafting existing customers while at the same time giving new customers an unrealistic experience.
Many sign up thinking they are going to be saving a lot of money by going with Netflix, but if their main interest is new releases then they are going to have difficulties getting every new release in a timely manner. This is something that Netflix doesn't really disclose very well & they are a little misleading with their marketing as you'll often see them promoting mainly new releases in a lot of their marketing material.
One more thing is that Netflix has gone as far as hiding certain new releases on it's New Releases section on purpose so as to prevent people from being able "hog" all the new releases. This seems rather anti-customer & goes against their original motto "Connecting People With Movies They'll Love", which really boils down to "We want you to use our recommendation engine which steers you towards movies that cost us the least...".