The iPad's UK page used to say "Coming late April." Today that was changed to "Coming late May." The good news is that Apple has set a pre-order date of May 10th in the UK, Canada, France, Australia and Germany.
In a press release today, Apple said that the iPad's US popularity is to blame for the lag: "Demand is far higher than we predicted and will likely continue to exceed our supply over the next several weeks as more people see and touch an iPad." Apple also said they sold more than half a million iPads in the first week.