Since I have been using Google docs I found it hard to believe that Google does not sync it with a folder in desktop. Documents being online is great and I love gDocs for lot of its nice features, but not having a copy on the desktop is a serious handicap.
Syncplicity solves this problem. More importantly, very easily too and in a couple of clicks.
Unfortunately, it just syncs docs but not XLS yet. But I am sure/hope it will supported soon.
~Sri