Compress PDF

See nice description here. In short using the command bellow on my Linux box (Windows users see PDFCreator) allowed me to reduce scanned color PDF for a factor of 4 to 5, e.g., from ~14 MB to  ~3 MB. Supposedly PDFCreator also 

gs -sDEVICE=pdfwrite -dMaxSubsetPct=100 -dPDFSETTINGS=/ebook -sOutputFile="out.pdf" -dNOPAUSE -dBATCH "in.pdf"

Update (2012-01-16): you can get a nice shell script called compressPDF.sh that saves some typing and can process multiple files, e.g., 

compressPDF.sh file.pdf