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I answered this age-old question by re-formatting my 2-page resume into something more "functional."
I put my education first, followed by all my experience in my current field, then, on the second page, I have an "Other Experience" section for all the experience that isn't directly related to the career (including volunteer work, etc), followed by an awards and research section. That way, when someone in my current field scans my resume, they can see all my accomplishments that would matter to them....and if the reader is intrigued enough to go on to the second page, they can get more of the "filler" experience that is interesting for them to know, but not quite so "essential."
So my resume reads like this:
Name, Address, etc
Education
Experience in [my field]
---Page Break---
Other Experience
Awards and Research
Note that, within each "Experience" section, the positions are listed in reverse chronological order, just like on a regular resume.
Overall, in answer to your question, I think that it is becoming acceptable to have a 2-page resume, if your experience justifies it. The important thing is to make sure that it is well-formatted, consistently organized, and thoughtfully-written.