Ever since a recent upgrade (I'm currently on 4.2.0.187, and about to upgrade to latest version), Skype hasn't been starting when Windows 7 x64 starts.
Looking at msconfig, I could see the following startup entry:
"C:\Program Files (x86)\Skype\\Phone\Skype.exe" /nosplash /minimized
Note the \\ where there should only be \
To fix this, open regedit and browse to:
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run]
Then edit the value for the key by double clicking on it, and remove one of the slashes before Phone\Skype.exe...
How to stop Skype (or any program) from autostarting:
If Skype is autostarting and you want to stop that from happening, simply delete the entry for Skype under[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run]