The X10 is a wonderful little camera. Full metal body and dials to boot. The issue that you are referring to, is the "white orb" issue that the first X10s had. The did not appear in every photo, but they appeared nevertheless - i believe you would have had to be shooting under specific conditions. Anyhow, Fuji came up with a fix, which was to replace the sensor for people who were able to demonstrate the problem. Fuji started to produce the X10 with the new sensor with cameras that had a serial number starting with 22. Therefore, if you want to be trouble free, i would inquire about the serial number. Further, if the serial number starts with a number below 22, i would inquire whether or not the sensor and lens assembly have been replaced under Fuji's warranty program - it was a free replacement.
The X20 is certainly a good camera as well, with an actual "overlay" in the OVF to display information. The OVF on the X10 is nothing but a glass tunnel. The X20 also has a somewhat different JPEG engine and gives a slightly different "feel" to it's JPEG's.
If i had the choice, i would still choose the X10 because of the EXR processing.
The X30 still has the same sized sensor as it's predecessors, much to the disappointment of some. It's a bit of a larger camera and has no OVF. Though, it has a lot of bells and whistles that are new to X cameras.
if you got the money, buy the X30. If not, be careful when buying an X10.
Good luck