## SAMPLE DATA
myDates <- c("2011-06-02T17:16:05Z",  "2012-06-02T17:16:05-07:00")


# CONVERTING

    format(strptime(myDates, tz="GMT", format="%Y-%m-%dT17:%H:%M"), format= "%m/%d/%Y %H:%M")
    [1] "06/02/2011 16:05" "06/02/2012 16:05"

    or with 2-digit year

    # Note the lower-case %y at the end
    format(strptime(myDates, format="%Y-%m-%dT17:%H:%M"), format= "%m/%d/%y %H:%M")
    [1] "06/02/11 16:05" "06/02/12 16:05"