There seem to be a couple of emoticons that aren't working, (text isn't substituted for the correct icon) below I've clicked on all the standard set of icons in order so you can see the two that only show up as text:
I haven't checked the extended set of emoticons as I don't generally use them, but I guess it's possible some of them have issues too, so might be worth someone checking.
The other issue I've had for a long time (forever ?) is that the background colour highlight of the message list in the notifications drop down is far too subtle - on some displays its nearly impossible to see which messages are unread and which are read. The contrast is more visible on my iPhone than it is on a Windows PC, perhaps due to gamma differences - on both my work PC and Windows 7 laptop at home the difference in background shading is so subtle I can't tell the difference.
It would be nice if the unread messages had a more obvious background colour contrast - sometimes I just can't work out which ones I haven't read yet and have to click mark all as read, which isn't ideal as I end up missing things I should be reading.