I always shut down my system at night and that includes first closing browsers, explorer, etc.
But I haven't had any issue on my desktop XP Pro system.
My win7 netbook just goes into standby and if the browser happens to be open it stays that way, my last sync was a couple of minutes ago when I woke it out of standby/sleep and viewed the browser. This system however, doesn't have the beta build if this might be an issue.