Singularity Sky by Charles Stross.
An entertaining if uneven romp through a universe where nanotech disrupts post-Tsarist colony worlds and where an uploaded civilisation does all it can do to prevent entities from changing the past, thus editing them out of history.
A big part of the book (a bit too long) is a hilarious sendup of the kind of neo-Napolonic space navies as described by David Weber in the Honor Harrington series.