Search notes:

Registry: HKEY_CURRENT_USER\Software\Microsoft\Office\_version_\Excel

Values found under this key might be:

AutoSaveInterval
ExcelName (which, not so surprisingly is Excel in my installation)
FontInfoCache

Subkeys might be:

AddInLoadTimes
File MRU
Options
Place MRU
Recent Templates
Resiliency
Security (Which contains the subkeys Trusted Documents and Trusted Locations
User MRU

See also

HKEY_CURRENT_USER\Software\Microsoft\Office\X.Y