I don't see any problem in using them as another study tool, as long as you don't solely rely on them. As Cstorms said above, they a) use the exact questions that are on the test and b) sometimes don't give the right answers. If you use them as your only study tool to get the cert, when you get out in the real world you will be weeded out as only having a "paper cert" (or whatever expression you want to use). You will not last long in the IT world (that is if you can even get past a techincal interview). It's really, really, really easy to spot the people who know the material from those who just used a brain dump.
My suggestion. Use it after you have already studied and mastered the material. No harm in looking them over after you have put in the work.
A+, Net +, Security +, onto the CCNA