Due to its weight, I found it physically difficult to pick this book up. Due to its plot, I found it very difficult to put down. Here we have bits of Neal Stephenson's Baroque trilogy, except with all the improving stuff about economics and mathematics replaced by magic. (No doubt the fact that I say that indicates my embarrassing ignorance of Jane Austen.) Here we have friendship, rivalry and reconciliation against the background of the Napoleonic wars as they never happened. And the alternate military history reminds me a bit of Mary Gentle's Ash, though that book challenges the received version by introducing women rather than wizards.
Coincidences are weird things. Susanna Clarke's name is a lengthened version of my ex-girlfriend's (they are different people though as far as I can tell). The novel features a Captain Whyte in the Peninsular War, a conflict in which my great-great-grandfather, Nicholas Whyte, lost two of his brothers. (Fascinating interview with her here; also interviews with Jonathan Strange and Mr Norrell themselves.) All very strange, yet compelling.