I have seen the same problem twice in the last 5 days or so. Normally we receive about 500-700 clicks a day. Yesterday on 1-04-04 we received 0 clicks. Today we are getting some clicks. Our most important keyword used to bring us up on the adword for every search done for that word, now we rarely show up there even though we are paying more than anyone else. Perhaps it has something to do with the fact that we also run adsense at our site and may have broken a rule- I don't know.