Way late to the game, but from what I can tell there's not much happening for the cart
package; my recent efforts with cartogramming in R have pushed me towards two alternatives: Rcartogram
within R (available from the GitHub repository) and ScapeToad, a program written in JS.
Advantage of the former is that you don't have to leave R (better for long-term project management), however it's a bit arcane to use (requires converting your shapefile to a density grid & then figuring out how to use an interpolation method, etc.).
Advantage of the latter is that it's got a very simple point-and-click GUI--add shapefile, create cartogram wizard, export shapefile, voila.
Both are based on the Gastner-Newman diffusion-based algorithm.