In version 0.8.1beta, when I modify some settings in the preview, and save them under a different name by clicking on the "Save preset" button, then the next time I start Gephi, the preset is no longer there. All entries below the "---" line are replaced by items called "Default", and selecting these does seem to yield the default preset, i.e. the settings are gone.

[so, my list of presets now looks like this: ]
Default
Default Curved
Default Straight
Text outline
Black background
Edges Custom Color
Tag Cloud
"---"
Default
Default
Default

[my system info: ]
Product Version: Gephi 0.8.1 beta 201202141941
Java: 1.6.0_31; Java HotSpot(TM) Client VM 20.6-b01
System: Windows XP version 5.1 running on x86; Cp1252; en_GB (gephi)
User directory: C:\Documents and Settings\koa\Application Data.gephi\0.8.1\dev
Cache directory: C:\Documents and Settings\koa\Application Data.gephi\0.8.1\dev\var\cache