After installing 11.10 the behaviour of my keyboard changed. I now suddenly need to press spacebar after typing some special characters like quotes to make them appear. How can I fix this? This wasn't the case in 11.04.
It sounds like you have a keyboard layout with dead keys selected. In this mode, pressing " followed by something like a will generate the character ä. Pressing Space cancels the dead key behaviour to give you a plain quote character.
You can turn off dead keys support as follows:
Found this question from googling on my issue - having to press tilde twice to get it to print out. I think what James said should work perfectly. However, in case you're not running GNOME - e.g. I'm on Xubuntu - this achieves the same thing:
sudo dpkg-reconfigure keyboard-configuration
Then you go with one of the generic models, see the difference between 101, 104, 105 keys here: http://en.wikipedia.org/wiki/IBM_PC_keyboard
I went with 104, no dead keys, en-us. Rebooted and it works like a charm.