Emma,
Since [at least as far back as records go] all Ardiff's come from Leixlip, I'm basicly doing a surname study on them. My mother-in-law is an Ardiff living in Clondalkin, henace the interest.
I have been working with a 4th cousin of my wife that was born in Leixlip and we have done a fairly good job with the Ardiif's in Ireland, but there are at least two branches that came to America in the mid 1800s. They are fairly well documented in America and I have been able to go back one generaltion in Ireland on both branches. I just can't find records to tie them in with the main branch that stayed in Ireland. We know they are related, we just can't officaly figure out how.
I have been purchaseing/collecting all Ardiff records (whether there is a known connection or not) on Findmypast.ie, RootsIreland.ie, irishgenealogy.ie, familysearch.org and various other sites. I have large spreadsheets and charts to show all the data so that I can look for cominalites between the records.
I have also been to the GRO many times collecting records, as well as the National Archives and the Dublin City Library. I have even talked with Eibhlin Roche, Archive Manager, for the Guinness Archives, since the origanal brewery and estate was in Leixlip. I have also spent a few mornings in the Confey cemetery and the cemetery in Maynooth.
I still need to look at probate records and land records a lot closer.
I'm hoping someday to tie these stray branches in. In the meantime, I'm happy to talk with anyone that may be able to fill in some of the 'newer' branches.