My family research, which began in 1990, now covers much of England (Cornwall, Devon, Hampshire, Sussex, Essex, Rutland,Leicestershire, Nottinghamshire, Derbyshire, Durham, Kent, Northumberland etc), the Shetland Islands,& County Wexford, Republic of Ireland.
The most detailed research I have is on the Christian family of Rutland & Leicester, the Coe's & Parr's of Nottinghamshire,the Slater/Sclater/Slatter's of Shetland, & the Smith's & Cooper's of Kent (i.e.Bexley Heath)
A cousin of mine, Enid Hargreaves, has written a large book on this last families' history. I believe it is available for consultation at the Bexley local history library.
Apart from illigitemacy, the biggest mystery I have is that of my 2x gt grandfather James Slater (b.Walls, Shetland 1808) who vanished on the Baltic island of Osel (now Saaremaa, part of Estonia) in 1849 after the brig he was master of was driven aground there!