Normaly autoindent is enabled, so it looks horrible when you paste something from an webpage into vim. So before you do this, type:
Then in insert mode you can paste as usual with Shift+Ins.
Edit: Caution! This disables mapping in insert mode and in command-line mode and abbreviations !!
So to disable it again type :set paste! or :set nopaste.
Another method and much faster is to type:
paste the code and hit CTRL-C.
Hint: Hit enter before CTRL-C if you did not cut the last \n to not to miss the last line.
What annoys me too sometimes is the auto-commenting of vim, you can disable it with:
But this only works when you type it in command mode. To set it permanently, you have to write this in your ~/.vimrc :