That depends on if you are a mathexpert that needs the wonders of Excel... Pages = Word for educationpurposes and in some cases even exceeds it. But Keynote is so far ahead of Power Point that it's no use discussing it.
iWork works better with student is my experience... and with the pricing, in Sweden that is, for Ms Office vs iWork there is no way I would use Ms Office. For my school we pay 2750 SEK for iWork 09 as a one time price and at best for Ms Office 2010 we would have to pay 154 000 SEK per year!!!
We are in a 1-1 computing environment and we do not have IWorks on our computers. We have the ILife suite which is really important for us, but we felt using Office was a better solution. Most people are familiar with Office, and students will be doing their work in Office, Excel, etc. throughout the academic career, and therefore we thought it made more sense to develop their skill in just one set of programs. I personally do not see any drawbacks to not having IWork.