If you are using any SCM that allows cheap branches (like Perforce) and are following the advices from the High-level Best Practices document, you might be interested in (or already know) Laura Wingerd’s presentation Convergence vs. Divergence: Purposeful Merging with Perforce about how to converge to codelines using Merge Down, Copy Up [PDF]. I have seen it many times that a main codeline got broken because the Merge Down, Copy Up idiom was ignored.

Longtime Apple developers probably know this intuitively, but I needed some time to figure it out: When CVS-ing files with a resource fork, you must not use the /usr/bin/cvs that ships with OS X!

Because Apple used to separate data and metadata, most files in the pre OS X era had a data fork and a resource fork, but for the user this was transparent; the user just manipulated one file. Tools without this “Classic” background know nothing of the resource fork. Files without data fork appear in the Terminal to have 0 bytes.