Merriam-Webster's Eleventh Collegiate Dictionary (2003) is now eighteen years old, and—as far as I know—Merriam-Webster has no immediate plans to issue an updated Twelfth Collegiate. The gap is striking, since previous editions of the Collegiate series tended to come out at ten-year intervals. Here are the dates of release of the eleven editions of the Collegiate Dictionary:
First edition: 1898
Second edition: 1910
Third edition: 1916
Fourth edition: 1931
Fifth edition: 1936
Sixth edition: 1949
Seventh edition: 1963
Eighth edition: 1973
Ninth edition: 1983
Tenth edition: 1993
Eleventh edition: 2003
So the longest previous gaps between editions were fifteen years between the third and fourth editions, fourteen years between the sixth and seventh editions, and thirteen years between the fifth and sixth editions. It is also noteworthy that the backbone of all editions of the Collegiate Dictionary since the seventh edition (1963) has been Merriam-Webster's Third New International Dictionary (1961), which is now sixty years old. The release dates of major revisions of this full-size dictionary and its predecessors going back to Noah Webster's first An American Dictionary of the English Language are as follows:
An American Dictionary of the English Language: 1828
An American Dictionary of the English Language, second edition: 1840
An American Dictionary of the English Language. new revised edition: 1847
An American Dictionary of the English Language, royal quarto edition: 1864
Webster's International Dictionary: 1890
Webster's New International Dictionary: 1909
Webster's Second New International Dictionary: 1934
[Merriam-]Webster's Third New International Dictionary: 1961
Meanwhile, new editions of The American Heritage Dictionary of the English Language have appeared in the following years:
First edition: 1969
Second [College] edition: 1982
Third edition: 1992
Fourth edition: 2000
Fifth edition: 2011
A couple of years ago, the consultancy where I work as a freelance editor switched its in-house dictionary from the Eleventh Collegiate to the fifth-edition AHDEL, specifically because the staff editors there were concerned that the Eleventh Collegiate was falling out of date and was less likely than the AHDEL to be refreshed in the near future. We shall see whether a sixth edition of AHDEL comes out in the next two or three years and justifies that decision. In any case, AHDEL fifth edition is eight years younger than the Eleventh Collegiate.
All of the many U.S. publishing houses that I've worked for over the years have used either the Merriam-Webster Collegiate series or AHDEL as their in-house dictionary. Another major U.S. dictionary option is [Random House] Webster's Unabridged Dictionary of the English Language (2001), which is an update of earlier full-size Random House dictionaries (from 1966, 1987, and 1993).