Constitutional Conventions are more common than some might think. There are actually fourteen states who have automatic calls for a Constitutional Convention every so many years as a check on government and many states have updated their constitutions in recent decades.

Recent Conventions

Montana
By 1967, a consensus opinion emerged among the Montana electorate that the 1889 Constitution had aged poorly, and the institutions of state government needed to be revamped. That year, Montanans voted for a constitutional convention to do just that. Revisions were mostly centered on political reform, like forcing legislative sessions into the public record whereas the legislature previously operated from behind closed doors. More contentious reforms included moving the legislature to meet annually instead of biannually, and the establishment of bipartisan citizen committees to handle reapportionment.
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Hawaii
Constitutional Conventions have been relatively commonplace throughout Hawaii's young statehood. Delegates to the 1949 convention drafted what would, in 1959, be accepted by the US Congress and President Eisenhower as the first official constitution for the newly admitted US State of Hawaii. A decade later, another Constitutional Convention was called to address the deficiencies of the 1949 document, and a second Constitutional Convention in 1978 finalized the Constitution that is still operating today.
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Illinois
During the general election of 1968, the voters of Illinois voted overwhelmingly (72.5%) in favor of calling a State Constitutional Convention. A Convention was convened the following year, where the 6th Constitutional Convention of Illinois drafted a new Illinois State Constitution, which became law after final approval by Illinois voters in 1970.
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Michigan
The Michigan State Constitution is Michigan’s fourth constitution. It was drafted during the 1961-1962 Constitutional Convention, and approved by voters in 1963. According to the 1963 Constitution, Michiganders hold a Constitutional referendum every 16 years, the next scheduled for November 2010. The document which resulted from the 1963 convention was narrowly ratified by the Michigan electorate, winning by a margin of less than 7,500 votes and surviving a statewide recount. The quality of the 1963 constitution has since been legitimized by two overwhelming “No” votes calling for new Conventions in 1978 and again in 1994 (defeated by 70% and 72% margins respectively).
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Connecticut
In the 1964 case Butterworth v. Dempsey, the US Supreme Court ruled that Connecticut's “borough system”, which had been hardened by the 1818 Constitution, violated the principle of “one-man-one-vote”. The State was ordered to make the necessary constitutional changes, and, after much resistance and haggling in the Connecticut General Assembly, a convention was finally convened in 1965 to focus on its mandate: reapportionment. Convention delegates proposed 271 resolutions during the convention; 23 proposed procedures for conducting the convention while the other 248 proposed changes to the
underlying state constitution of 1818.
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State Constitutions

http://en.wikipedia.org/wiki/List_of_constitutions_of_the_United_States