Once you enter the Big Tent of Apple, it's exceedingly hard to find the exit.

Over its 33-year history, Apple has consistently elected to limit consumer choice, creating a situation known as "lock in." As soon as you start buying stuff from Apple, you'll find it difficult to move to products made by someone else without losing everything you've already paid for.

Of course, many people don't want to leave Apple's tent. After all, it's filled with iPhones and MacBooks and other cool stuff. And Apple is hardly the only business that tries to lock in customers--wireless carriers (including Apple partner AT&T) are probably the worst offenders. Nor is Apple the only vendor to use one product as leverage to push others onto consumers (let's declare Microsoft the champion there).

But no other technology company exercises the same amount of control over what its customers can and can't do with the things they bought. Part of this approach is due to Apple's deep belief that a closed digital ecosystem with limited options benefits both Apple and its customers. Part of it is due to an all-consuming desire for control on the part of the ringmaster, otherwise known as Steve Jobs.

The bottom line: Apple makes great products, but its marketing practices limit your choices and cost you more money. Here are five classic examples of how the company has done it.

1. iPod and iTunes

When the iPod arrived in fall 2001, followed by the iTunes Music Store in spring 2003, few early adopters realized the commitment they were making by buying their media player and their media from the same source.

Due to Apple's digital rights management setup, until April 2007 any music you bought from iTunes could play in only three places: on an iPod, within registered iTunes software on a limited number of computers, or on certain Motorola phones (that nobody bought).

If you wanted to move the songs you bought at a buck apiece to a cheaper player from a competing manufacturer, you had two options: an onerous process in which you burned your songs to a CD and then reripped them as MP3s, or quasilegal software that essentially did the same thing using your hard drive instead of a disc.

The last vestiges of DRM-protected music vanished from iTunes two years later. Apple offered to remove the DRM from the music that iPod owners had already bought, as well as to bump up the sound quality, for an additional 30 cents a track. (Gee, thanks, Apple.) Of course, movies and TV shows sold on iTunes are still copy-protected and cannot be legally converted to a DRM-free format.