To quote myself, "...I still occasionally pipe the results of find through grep -v and then on to something else..." I agree find is greatly useful for the purpose of finding files (I don't know how Windows sysadmins could live without it) and learning its basics is important in one's mastery of the shell, but it's clearly "not like the others". It has useful options to control its behavior like outputting with null separation (something I wish `ls` had), following symbolic links, searching up to a maxdepth limit, and limiting the type to file or directory. And in the same way you can make justifications for the utility of other `find` features, but for nearly all of them and the ones I mentioned they have an irregular syntax. There are also things that obsolete `find`'s features like `xargs` that are simple to use and easy to understand and are useful in more contexts than `find`, even if using them has some performance hits. (And `locate` obsoletes `find` almost entirely because of performance when you need to search big swathes of your system.)
I think Ritchie sums up my feelings for `find` with "...we were somewhat put
off by the syntax of their things. However, they were clearly quite useful..." `find` is useful, it's just not Unix-y. Does it still follow some of the Unix Philosophy in spirit? Maybe. I think there's also a chance that Unix Philosophy in its purest form is mostly dead in practice and has been for a while. Just look at the evolution of echo.c: https://gist.github.com/1091803
I'll readily agree that `ls .. | grep -v ..` can break, but I don't find anything archaic or non-Unix-y about it like I do with the `find` version. (Also every time someone uses `cat .. | grep ..`, a kitten dies. :( )
Finally, it's not the newbie-unfriendliness that `find` has, it's the irregularity and kitchen sink of features that aren't expressive and don't generalize well, as the other repliers elaborate on. In my experience `sed` and `awk` are more regular, more generally useful, and have less "intuition traps" than `find`. (As sort of a neatity aside from their surface-level expressiveness, both sed and awk are Turing-complete. I think it's interesting that my man page for sed(1) is 267 lines, my man page for gawk(1) is a hefty 1713 lines, and my man page for find(1) is also a hefty 1446 lines.)