I have tried using SB28 with FZ10, the result was excellence, after upgrading to SB800 (for my Nikon D70), I also get excellence result:
1. In FZ-10, I set the external fresh mode to Manual, this is important, if not when FZ-10 detects an external fresh, it will set everything to auto, that is: ISO100, F2.8, speed 1/60.
2. I usually set the dial to "ASM", and in the menu I select "Apperture". My favourate setting is ISO200, I usually set apperture manually and let the camera adjust the speed accordly.
3. Ensure that the SB800 or SB28 is set to ISO200, Apperture must be similar to that of the camera. FZ-10 speed setting is aways default to 1/60 when external fresh is detected unless you use speed priority. Fresh must be set to Auto mode, TTL mode will not work in this case.
4. I guess similar methology should apply to other fresh. It must be an Automatic fresh, ensure you set the FZ-10 similar to "1" above. Ensure ISO and Apperture is similar to FZ-10 setting, it should work perfectly.