So I've been having fun trying to squeeze out space on my 2TB drive.
As I tend not to waste space, and thus, all the 'low hanging fruit' space saving techniques have been done (eg 7z'ing up old stuff), I've turned to more drastic measures.

So far:

• re-encode the video of lecture recordings (10GB » 5GB), as it seems to be fixed 128kbps 1fps H.264 using QuickTime, so hell inefficient.  Can't do much about audio (32kbps LC-AAC)
  
• I happen to have some World of Warcraft install files + patches, totalling 15.4GB.  I noticed that there's some zlib streams in there, so I tried applying precomp to it, expanding it to 27.6GB, indicating that there's a fair bit more than just zlib (but can't do much about that).  After LZMA2, goes down to 11.6GB, about 4GB saved
  
• Currently running packJPG on several GB of photos/pictures.  Unfortunately the GUI seems to refuse to process more than about 49 files at a time, so I'm chunking things up.  Maybe I'll write a script to do the rest instead >_>  I'm getting around a 30% saving over the JPEGs captured from the digital camera, so quite good, especially considering it's lossless.  There's no .pjg viewer unfortunately.  Maybe I'll write a XnView plugin for it some time...  Should save a few GB
  

I shall continue!

(lol at what I'm doing to save a few GB)