Blogs that you know have updated but the updates don't show up on your computer for 48 hours or longer. I have had some blogs updates not show up for a couple of weeks and this from people I know generally have something to say daily. I will hit refresh, restart my computer but nothing seems to work. I just have to be patient.
One of the worst things though is missing something that you would want to comment on and seeing that somehow many people were able to comment ahead of you so you know that they don't have the issue. Arrrggghh.