While still on Android 1.6, the latest update for the Sony Xperia X10 introduces a new wifi bug. This bug is getting on people's nerves so badly because when they are located in an area with poor cell reception, they cannot access data on their phones with wifi! Never mind the fact that you probably rely on WiFi working most in areas where reception may not be there, if your signal happens to drop down to zero bars then gets wind of a good connection and the bars jump back up, out goes the WiFi. The issue has only appeared in phones that have gone ahead with the R2BA026 update.
Here is a video that shows the bug perfectly. Xperia users, stay clear of the super fail update and wait for a fix from Sony Ericsson.