The new Google spreadsheets use a different URL (just copy your <KEY>):
- New sheet :
https://docs.google.com/spreadsheets/d/<KEY>/pubhtml - CSV file :
https://docs.google.com/spreadsheets/d/<KEY>/export?gid=<GUID>&format=csv
The GUID of your spreadsheet relates to the tab number.
/!\ You have to share your document using the Anyone with the link setting.