Although the text editor of the Effective Altruism Forum works well for most users, occasionally people have problems with text formatting.
The main trick is to be careful of text that you have pasted in from another document. When you paste text, its original formatting is preserved and this will generally not match the rest of the forum. You can correct the text by correcting the html by hand, or by using this site to convert your html to plain text.
For advice on formatting comments correctly, click the 'Show help' button at the bottom right of the comment box. It tells you how to do italics, bold, links, bullet points, and (most importantly?) how to do block quotes from the comment you are replying to.
(Images are broken.)
In Chrome for Windows 8, images are broken.
fixed
This may be just me, but it would be handy to be able to input in markdown as well as html. It seems pretty common to have editors that accept both.