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Last Friday afternoon I undertook the Salesforce Advanced Administrator Certification exam (a.k.a. the 301) — I was reasonably comfortable going in, though did wonder what boundaries of my knowledge it would push. Having done other exams in the last two months, I'm very much in the mind set required and that's a definite help, this exam took me the least time of all those I've tackled so far.
Advanced Administrator builds on top of the Certified Administrator exam, testing in finer detail your knowledge of things like platform security, and how features related to that work, for example the Role Hierarchy. What surprised me about this exam was that involved a reasonable number of questions regarding the force.com platform, for instance, what components may or not belong to the platform and what Visualforce does and doesn't offer. Clearly the thinking here is that an Administrator should know what development-heavy customisations to the platform involve and impact, even if they can not create and maintain those customisations themselves, but it surprised me mainly because there seemed to be more questions on such topics in this exam than there were in the Certified Developer (401) exam.
It's hard to offer any other advice other then the comments I've made, you simply need to know the areas outlined in the study guide. One thing I do in the exam (which doesn't help you pass but does let you get some idea of how you may have done) is to use the scratch paper to create 3 columns, one labelled with a tick, one with "?" and the last with "??!". I then write down a tally mark for each question, the first column are those I know I've got right (or I'm at least 99% sure and would be surprised if I had wrong), the second those I'm pretty sure I've got right but I'm not entirely confident, and then the last column is for those where I genuinely have no idea (luckily these are rare, I think I had 2 in this exam). For all the questions in the latter two columns, I check the box saying "mark for review" and those are the ones I pay special attention to on my second pass through. This time, just before I hit submit I worked out that 72% of the questions were in my first column, and I think 24% were in the second so unless I was wildly out (and I'm pretty strict with myself!) I stood a good chance of passing. Like I said, this doesn't increase your chances, but does give you a rough idea of how well you might have done.
Remember, always read the questions carefully (there sometimes something in the question which will tell you the correct answer), and think about what answer may entail before reading the options presented: there's nearly always something designed to make you second guess yourself and it pays to have already considered what the correct answer(s) will be.
Lastly, too all of those taking the exams, good luck!