The DISQUS commenting system is very powerful, but it does have some limitations. Two of the most notable limitations are a lack of a rich text editor and the default size of the comment textbox. These shortcomings can be worked around with a couple of Firefox add-ons.
To compensate for the lack of a rich text editor, I recommend the BBCodeXtra add-on. It can be downloaded here.
The add-on Text Area Resizer & Mover is my recommendation for enlarging the textbox. It can be downloaded here.
If you aren't already using Firefox-what's wrong with you?-it can be downloaded here.