I had a blog with WordPress 2.8.1 and used the built-in automated update to go to 2.8.4.  Suddenly the process stopped at the point where it says “Installing the latest version.”  I left it for a half hour, but when I came back it was still stalled.

I tried clicking on the dashboard and saw this message:

When I clicked on the link to try it again, the update happened quickly and fully without any problems.

This was the first 2.8.4 update that hasn’t gone smoothly for me (I’ve done over a dozen from 2.7.1, 2.8.1, and 2.8.2 without any glitches).  Some other people haven’t been so lucky – see the update tag on the WordPress forums.

Common answer on the forums is:

3. Try adding this line to your wp-config.php file:
Increasing memory allocated to PHP
define('WP_MEMORY_LIMIT', '64M');

[from this forum thread]