I use Firefox as my browser. I have upgraded it to the latest version and now, my English will be spell checked for me in a real time fashion. The thing I probably will like best is, that a word like "localising" is now seen as correctly spelled. This is because Firefox allows me my British English. Blogger, although nice expects people to use American English spelling. This is useless when I were to blog in any other language.
Another thing that is nice is, that it allows me to accept words that are correct in the texts that I write; WiktionaryZ is such a word .. and so are MediaWiki, Wikimedia and Wikipedia.
By having spell checking done client side, the server functionality becomes cheaper for the service provider as well. The quality goes up.. all in all a good reason to upgrade to the latest Firefox.