There won't be any research required! It'll all be available instantly from a wristwatch sized doohickey implanted somewhere.

Perhaps some of these won't happen until 2108 but they could still be theoretically be possible.
Everyone's DNA will be in one huge global-tree database with all of our brick walls knocked down.They could get DNA samples from:
The PKA blood samples that have been taken from newborn children for decades (that's the prick on the heel they do to newborns).
Any letter you or your ancestors have ever sent might have DNA on the back of the stamp or the envelope flap. Letters from any identifiable historical figures will also be sampled.
We can already obtain DNA from woolly mammoths. Graveyards will become valuable sources of historical information.
My descendants will know who my second gt gran Diana had two illegitimate children with.
Every visit you made to every shop and what you bought throughout your entire life may be available, especially if you paid with plastic.Instead of '
where was gt grandma in 1861?', they will be asking '
why did he buy a pregnancy test kit from Boots in dd/mm/2008?'.
Medical records may be available.I recently discovered (from his army pension records) that my grandad was only 5'4''. They might be able to gain access to my X-rays!!
Online traces.Every e-mail you've ever sent. Every phone call you've ever made. Every website you've ever visited.
Well, perhaps not, but that would be a pretty scary prospect wouldn't it?
This post might be discovered by my 7th gt grandchild. He/She/It will probably have a huge laugh at my naivety.
I certainly don't want to be around then.

Paul