Also, there have been changes to item rendering. RenderItem has been changed to require a TextureManager and ModelManager argument, but you can get an instance of the RenderItem in Minecraft#getRenderItem(). It appears the rendering bit isn't deobfuscated, but RenderItem#func_175042_a(ItemStack, int, int) will draw your item. Args: item stack to draw, x coord, y coord. This also seems to draw any effects, combining the two separate methods in 1.7.
GuiScreens can now throw exceptions on key and mouse inputs, so those will need to be handled accordingly too.