I've just checked in the first step for using places history in SeaMonkey
"Places" is the new SQLite-Database-backed scheme for saving URLs of any interest which is built into the Mozilla toolkit and is already used by Firefox (for browsing history, current Firefox3-preview-nighties also use it for bookmarks). Our target is to use this component at least for history in SeaMonkey 2 instead of the mork-backed xpfe history we still have in use for now.
The current patch makes it possible to build SeaMonkey with the places backend with the --enable-places configure option. URLs from old mork history will be automatically imported into the new places.sqlite file in the user profile, visited links and the urlbar autocomplete popup work without any further work, but the history window and sidebar stay empty, as they are based on RDF templates which don't work with SQLite/mozStorage. mozStorage-based XUL templates
should make it easier to get them working again, once those make it into the toolkit code.
I hope some people who are doing builds themselves will enable the new backend and do some testing despite those UI bits not working so that automigration, urlbar autocomplete etc. get their share of testing before we fully switch to the new scheme.