Using the get method allows the form submission to be contained completely in a URL. This can be advantageous in that it permits bookmarking in current browsers, but it also prevents form data from containing non-ASCII characters such as "é" and "©". As well, the amount of form data that can be handled by the get method is limited by the maximum length of the URL that the server and browser can process. To be safe, any form whose input might contain non-ASCII characters or more than 100 characters should use METHOD=post.
With a METHOD value of post, the form input is submitted as an HTTP POST request with the form data sent in the body of the request. Most current browsers are unable to bookmark POST requests, but POST does not entail the character encoding and length restrictions imposed by GET.