The way I look at it, if you know the material but are not necessarily a great test taker (some people have a load of "common sense", aka "street knowledge", if you will, and can configure the you-know-what out of a router but cannot pass the test), there is nothing wrong with practice questions. I am one of those people, actually. I can read a book and get it, and I know my stuff (sort of) when it comes to Cisco, but I am not the best test taker. I can go through any interview and pass their tests after the HR interview---ask Cluebird or CiscoGuy about what sort of interviews I am talking about.
How2Pass has questions that are similar to the actual test, I admit, but they have a forum to ask questions about the material and in order to pass their test, you have to know your stuff. Get around a 90% on their test, and you're good to go. Some organizations require their employees to be certified (for example, to obtain a partnership level with Cisco to be an actual reseller and support entity). I know CCIE's who can't tell you why it is a bad idea to plug a new switch into a network with STP configured without checking the revision and STP mode, yet they can configure the hell out of AppleTalk and Token Ring. I also know people that have no certs that can design multiple 6509 switch topologies according to Cisco recommendations, and can run circles around certain IE's. It is about 80% of what you know, and 20% of what cert(s) you have.
There are also people with certs that have labs they use daily, but have little professional experience...
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tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!