<p>After you start tracking the source of a bunch of open source software, how do you keep your code in sync? Run <code>svn update</code> every time you want to look at or play with the code?</p>

<p>It strikes me that it would be better to essentially start mirroring the code with (say) a <code>cron</code> job every night. Have people set up workflows to do this sort of thing? (With alerts when/if any changes you make to the code end up conflicting with the latest update?)</p>

<p>Or am I on my own? (I'm running Mac OS X but interested in general as well as specific solutions.)</p>

If your repository sends you an email every time someone checks in, why not have a program that checks for those emails and then updates the working copy at that time? This way you're always up to date. Caveats include needlessly burning bandwidth and the possibility of getting odd conflicts when a file you're working on gets updated.
Just updating once a day, or once every few days, is only useful when there are a limited number of people working on a project, all in disparate areas of it. When you've got more than five people, and the possibility that they are working in similar parts of the code, updating once an hour, or more frequently, is much better.