Ok, so right now I got calibre connected to my PRS-505, doing nothing, but still using 464 Mb of RAM!!!!
Is this normal? Doesnt really encourage me to keep it running in the background!

EDIT: Ok, so I restarted Calibre and now its down to 94Mb (+ 4 parallel processes of 18Mb each) . Seems the program is not cleaning up/freeing memory after performing operations like importing RSS feeds etc?