There are some great insights on the excellent Emblemetric blog, which analyses the cold hard numbers behind logo trends, spanning back to the 1950s. To find out whether monogram logos like the McDonald's “M” are rising or falling in popularity, or to see how colour trends vary over time, pay them a visit.
A particularly interesting recent post looks at the surge in leaf-based logos in the past decade and whether it is now tailing off. If so, is this because of a fall in support for the environment? Or simply that as victims of their own proliferation, leaf logos have become a cliché to be avoided?