I had to compile the pecl memcache today for work on my devel system. I already had MAMP installed so I just wanted to do a pecl install ... turns out that won't work. There's a few steps you need to do first. (Note: you must have gcc installed to get this to work. Also, I won't cover installing memcached, just compiling the pecl memcache extension and tyeing it into php.)

• Using PECL to add to MAMP (OS X)
• First download the right php source from php.net
  In /Applications/MAMP/bin/php5 create an include directory