I came home the other day, and had my computer notifying me about less then 2GB free space left. I fiddled a bit round with my data, deleted cache, sources, downloaded archives, etc. All went fine, had about 7GB left. Closed the lid, went to sleep and work. I got home today, and the same message waited for me on the screen again. I did a deeper folder size analysis, and found the truth. DROPBOX (2Gb package) CACHE was 15GB! In my home folder was a

.dropbox/cache

directory, which had several YYYY-MM-DD formatted entries. I deleted all, but the last 2 dates, and freed 10Gb's. If anyone finds a good way to prevent this hog, please leave a comment.