You will need to add a password to your account again.

You can do it using the same steps that you did to remove it, or from a terminal.

passwd

Sorry, but Ubuntu doesn't support well blank passwords (it does, the LiveCD runs with it, but usually the system will expect a password). Ubuntu security is higher than windows (is not only about user-root separation) and sometime this means it is less convenient. This is a design decision, a trade-off that you can like or not, but one that you must accept if you want to use Ubuntu, this philosophy is so ingrained in the system, that there are lots of places that expect it that way.

All that said, you can enable autologin, but it's not near as convenient as Windows i.e., as soon as you want to connect to a protected wireless network you will be asked for your password , because by default, wireless passwords are encrypted with your login password.

tl;dr: Ubuntu expects an user with a password. You can run it without it, but you will find some problems.