I can happily report that there is a command-line interface (CLI) to TortoiseSVN that let's you create a shortcut to update a given WC for you. If you'd place that in your startup folder, it would update your WC(s) upon login. Check Appendix D.Automating TortoiseSVN.
I created a shortcut svn_update in Windows to run TortoiseProc.exe from Program Files, using the WC as the start-up directory. And the entire command-line reads:
TortoiseProc.exe /command:update /path:"c:\subversion\io_se"