I just checked using a special hard drive management program how much space different file extensions took on my harddrive. .mp3 lead it with about 50 GB then AVI with 29 GB and MKV with 23. And that's only my E drive. Another 17 GB of mp3s on my D drive, as well as 23 GB of AVI. 2.5 GB of mp3 on my C drive, and 1.3 GB AVI.
That's only counting the major formats, and not a real definite number, but it looks like I have around 69.5-70 GB of mp3s, 53.3-54 GB of AVIs and 23 GB of MKVs. Not including the FLAC, OGG, M4A, MPEG, WMV, MP4, MPG, TTA, DAA, WAV, ISO, BIN and other assorted formats, lol. Damn.