How many times you wished you could edit your last VCS commit comment to correct a misspelling?
Now you will notice such mistakes because IntelliJ IDEA 10 checks the spelling in the comment field.
And it not just spellchecks the text, it runs the Spelling inspection on it and uses your custom dictionary too. Hit Alt+Enter/⌥↩ on an underlined word and fix it as you normally fix things in IntelliJ IDEA code editor.
Spellchecker is also enabled in other dialogs throughout the IDE, e.g. Search/Replace dialog.