I've been doing alot of programming in node.js and I like to play with undocumented APIs so it seems natural when I needed to do some spell checking I decided to use the undocumented XML API that Google uses to do spell-checking in the firefox toolbar. I published the package into npm (the package manager for node.js) so to install all you have to do is

npm install gspell

and its easy to check any text and it seems to be able to process pretty long strings the script below shows how to check a string of text it returns the result as the second argument to the callback function. Heres a JSON dump of the object it returns. in the array c there is an object for each spelling mistake. Ive actually augmented the results the api returns to add the word it found that it thinks was mispelled I used xml2js to parse the XML the REST API returns and request to make the http calls. If you know of any changes that should be made just fork the repo and make a pull request