For me the boot duration hasn't changed in any noticeable way, XP Desktop still boots in around a minute and my win7 netbook I haven't measured but it is quicker, but again no noticeable increase in boot times in the time that I have had it.
I didn't know about dragging in the win7 taskbar, I don't know if it would change loading order (boot sequence); though there would be little point (other than aesthetics) in allowing the dragging if it didn't have some effect.
On the XP system the avast tray icon has always been displayed early (but no drag and drop in XP), not so for win7 (about 3rd/4th), but the avast tray icon isn't the avast main service, avastSvc.exe, but only the means to get to the user interface avastUI.exe.
I too generally don't shutdown the netbook, just let it go into a deep sleep