Performance of raster package

Folks,

I have played a bit with the R "raster" package, and found it has an impressive 
list of features; however, its performance seems to be less than optimal when 
confronted with sizeable rasters (say, a 250MB GeoTIFF): a focal statistics that 
took less than a minute in GRASS, took 7 hours or so in R.

Is there anything I could do to speed it up (I already tried readAll before 
invoking the focal statistic function) ?

Regards,

Luca Morandini
http://www.lucamorandini.it