Well call me slow but I just realized that the built in Asp.Net Web Development Server allows you to recompile/deploy your assemblies without the need to restart the web server. This seems to have been available since at least VS 2005 so all this time I've been debugging through pages for apparently no reason... I seem to remember that closing IE would kill the web server while debugging, which definitely isn't the case (anymore?).
What's even more interesting is that Session data is preserved across deployments. Was hoping authentication would be as well but I haven't had time to test that properly.
I'm mostly using Asp.Net MVC these days which tends to mitigate the need to do the old login->browse->debug routine. Still handy to remember though