Opera is another good alternative to both!
However, I know that some people are using computers from work and may have *no* say on what browser or other software they access with, so it's not always a simple issue of browser choice.
I am not having the problem myself, and from the sounds of comments above it seems IE8 may be a common theme in the situation. Can't say for sure, but if it's only happening in some browsers for some members, and only at times, it could be something in that respect. I did some searching and found one link that may hold some clues:
http://social.answers.microsoft.com/Forums/en/InternetExplorer/thread/3fdd2b51-4efa-4495-be03-17b647dc61b2Apparently IE8 works differently than other IE versions, but does offer a "compatibility mode" where you can have it load sites in IE7 mode or whatnot. May be worth a try for those having this problem. Beyond that, I'd have to do more searching, and since it sounds more like a particular browser or other matter, it's likely something related to that. Please feel free to expand on the problem if it continues though.
A workaround for anyone having issues typing...in ANY browser, would merely be to load up a text program (Notepad, etc. would do fine....) in another window, type up your reply/post there, and then copy it into the text box just before hitting Post. You won't have all the smileys and formatting buttons, but for plain text it works great if ever need. I do know of a simple outside program that allows the basic smileys, etc. though too, and if anyone is interested in that, I can post a link for it. It's a good way to preview a post "outside" of your browser for a forum.
Anyway, sorry I don't have a better answer right now, but that's what I know at the moment.