Here is an excerpt from my book Polishing the PUGS: Punctuation, Usage, Grammar, and Spelling:
more than vs. over
More than is used with figures.
“More than one thousand people bought Tim’s book.”
“The grammar book has sold more than fifty thousand copies to date.”
Over refers to spatial relationships.
“The football soared over the receiver’s head.”
Over can also be used with amounts.
“I paid over five dollars for that book.”
(One could argue that the number of dollars you spent was more than five;
however, here “five dollars” represents an amount of money.)
NOTE: Some references consider this an outdated distinction; others (including The Associated Press) recommend following the traditional rule.
For more PUGS Pointers, order Polishing the PUGS: Punctuation, Usage, Grammar, and Spelling tips for writers from www.KathyIde.com.