It's not optimized for posting from an ipad right now but it should be possible. What version iPad are you using? I'll run some tests over the next couple of days. We do have some fixed planned that should improve the situation for all iPad users shortly either way.
I use the iPad almost exclusively. I have the latest iPad, latest iOS. In the boxes used for posting, you can't paste unless you are REALLY fast. You have to press to bring up the menu for [select/select all/paste], for example, but it disappears in a millisecond. If you anticipate where the word "paste" is, you can hit it, and 1 out 10 times you can be fast enough. I have seen this on other websites. The odd thing is, it's not in all text input boxes that this is a problem. For example, if I want to paste in this box I am in now [write message] it's no problem. But if I want to post a submission or post comments into a general review box [say, if I write my commments in Draft or Notes and want to cut and paste into the General Review box - can't do that.]
The problem seems to be in those text boxes where you have the ability to format text. In normal text entry boxes [like this one, or quickees, pasting is not problem] I think I detailed this problem in another post before.