Check out this beauty: next of kin are named as the legatee died in the testatrix's sister's lifetime, before the money could be shared out to her. This name's Frances Buck's daughter as Mary Lane, which we knew, but not for certain - it also confirms that there were no other surprise children for Frances.
You would look up the testatrix on http://www.findmypast.co.uk's Death Duty Indexes (IR27) which you can do if you know the year the will was proved and the last name of the deceased. Here is the entry for Rosamond Lane of Wymondham, confirming probate happened in Norwich in 1844 with the magic folio number (241) being given at the end of the line.
You can now go to the new IR26 catalogue at http://haine.org.uk/wills/IR26_catalogue.htm where you can thus identify IR26/1680 as being the one you need - see this snippet as an example.
I had about a dozen IR26 records I wanted to check at Kew and couldn't believe how difficult it was to get the appropriate references. One had to guess one's way around TNA catalogue by putting in what reference you THOUGHT might cover the required year and surnames. A few other people had had problems, or had considered making a separate trip to Kew purely to consult the printed catalogue. I spent two solid days in the heat making it my mission to extract the catalogue entries relating to IR26, which I was successfully able to do. At one point I was on a train from Doncaster to Newark Northgate, where I knew I had only 3 minutes to change trains. I shouldn't have even been in Doncaster but I guess I missed my stop. On this leg of my journey I was standing up, holding the laptop as I used the 20mins and fading battery for yet more valuable processing time. At one point I was struggling with four 200 MB files, with just my MS-DOS friend 'ssr' for company.
I did get to Kew last week with my reference numbers and a bill (not a phone bill - though it doesn't say so on TNA's site) and saw some pretty awesome records. My favourite is will of 4xgreat-grandpa Lancelot Gibson who leaves £50 to the representatives of his brother William Gibson, legacy to be paid after the death of his widow. These are named in the estate duty records as being: Mary Tate, Ann Gibson and two male Gibsons. I was able to find the marriage of Mary Gibson, Q3 1860 Carlisle RD, to Thomas Tait and corresponding entries in the censuses thereafter which seemed highly likely. For a long time I thought the 1860 marriage was too late as Lance was dead by then, but in fact though he was dead his estate carried on recording pertinent facts which are completely missing from the will. I could never have positively identified Mary Gibson were it not for this document, nor would I have known about the Tait connection, as the Carlisle marriage was nowhere near the Gibson heartland.
In the event I found out lots about 'Mary Tate', including obtaining a recipe book written by her granddaughter at the time of World War One.
John Lain's IR26 record listed the children of his niece, who, being a woman was given only a life interest in his residuary estate - the children are certainly not listed in the will
William Whittock's IR26 record shows the children of his late brother, who had died in Philadelphia. In the will the wording is terse - we certainly don't get the full married names provided here.
So, should anyone ask, YES, it is worth exploring IR26 records, but do make use of finding aids and get organised so that your day at Kew with the old books is a profitable one.