You need to understand that the Quicktime MOV format is really just a way of packaging into a file the video data from a variety of codecs (the compression algorithms). It’s like the Mac equivalent to Windows AVI.
One of those codecs is called “uncompressed” and as the name implies, offers no compression at all and consequently results in massive files (raw video takes a lot of space).
What size/type of video are you editing?
If you have to use high quality HD Quicktime (eg for Mac/FCP transfer) then try installing the Avid DNxHD codec which will provide high quality HD compression. Although the files will still be quite large, they are ideal for further editing.
If you want to render to small files for distribution, try the other codecs listed under Quicktime (click the Custom button) such as Sorenson, MPEG4 or MotionJPEG. You can try the 1Mbps or 3Mbps presets to get an idea of output file sizes.