Another recommendation would be the file_column plug-in (http:// wiki.rubyonrails.org/rails/pages/HowToUseFileColumn). It is lighter (though not necessarily better) than acts_as_attachement and also uses RMagick for image manipulation.
The RMagick documentation is clear on this - you must invoke the Garbage collector manually after RMagick processing, as Ruby doesn't track the RMagick memory used.
file_column does this, but if you do your own RMagick code, you must call GC.start once your processing is complete.
Which rules out the memory problem and proves the use of actually reading
documentation. 
