I am using Mac just since January and im still not so familiar with it. If you want to install latest memcached on Mac OSX you will need libevent.

Download libevent from this site:
http://www.monkey.org/~provos/libevent/

Then unpack, configure and compile it. Also install it in /usr/local

./configure --prefix=/usr/local
make
make install

Then obtain latest memcached from:
http://www.danga.com/memcached/download.bml

Then unpack, configure and compile. You need to point to the same folder so configure could find the library.

unpack
./configure --with-libevent=/usr/local/
make

./memcached -u root -vv 

And thats all.