This may or may not solve your problem.
Go to the Control Panel on your computer, which can be found on the Start Menu (at least, I assume it's still in the same place on Windows 7). On the Control Panel, double click the Regional and Language Options icon. Click on the Languages tab. Click on the Details button.
A window will come up. The bottom half of the window shows you the Installed Services. If there is a service called Voice Recognition, you can remove it (unless, of course, you are using or plan on using Windows' voice recognition features).
This installed service has been known to cause delays in typing, although I don't know if this is your problem or not. It's possible that a Windows Update reinstalled that service, but not very likely. It's worth a try though.
You also might want to try booting in safe mode. If the delay occurs while in safe mode, then the cause could be narrowed down to hardware issues, Windows corruption, registry corruption, or some sort of malware. However, if this started soon after the Windows update, then it's probably not any of those issues.
The only other thing I can think of is that the update has installed some sort of process or service that is running in the background and is using up your memory and/or CPU. You might want to press Ctrl + Alt + Delete and choose to go to your Task Manager. That will show you what processes, services and applications are running, as well as how much CPU and memory they are using. If anything appears abnormally high, then it may be hogging your system's resources and causing the delay in typing.
EDIT: It's possible that there is some sort of driver issue as well, but unless you've installed a driver recently (or Windows update installed a driver), then it shouldn't be that. If all else fails, however, I can direct you to a link from which you can download an application that will check your drivers.