Accesskeys in Internet Explorer:
Pressing an accesskey(Alt+KEY) when there is a selection, deselects it preserving the caret position.

Accesskeys in Firefox:
If there are multiple editors in the page, accesskeys(Shift+Alt+KEY) will work on only the first editor instance.
This is because FF does not allow dynamic adjustment of accesskeys.

CTRL shortcuts:
Do not use A(select all), C(copy), V(paste), X(cut) keys as they are text operation keys by default.
Do not use F(find), O(open), P(print) keys in IE and Safari as they will always fire their default actions.

New line character:
Since new line is represented by different characters (\r, \r\n, \n) on different platforms, there may be some
unexpected behaviour of the editor in some platform-browser combos regarding the cursor position after text
insertion/replacement. Specify new line characters as "\n", if you have to use any in your scripts.

POST variable limit:
Although it's a rare case, you may have to increase your server post variable limit if you have problems while adding too many buttons in admin interface.