Is this thing on? (How to tell if my cpuminer is working?)
You're using the wrong hash algorithm for Bitcoin mining. Bitcoin uses SHA256d (d = double), but cpuminer (at least the version 2.3.2 on my system) defaults to scrypt (for Litecoin) instead:

-a, --algo=ALGO       specify the algorithm to use
                      scrypt    scrypt(1024, 1, 1) (default)
                      sha256d   SHA-256d


Slush's pool is Bitcoin, so you should add -a sha256d to your command line. You'll see a much higher hash rate (scrypt is intentionally much slower to compute than SHA256) and you'll get yay!!! instead of booooo after some time in your log:

[2013-12-09 21:51:25] thread 0: 49985792 hashes, 832.61 khash/s
[2013-12-09 21:51:29] thread 1: 51072988 hashes, 841.16 khash/s
[2013-12-09 21:52:23] thread 0: 49956628 hashes, 864.18 khash/s
[2013-12-09 21:52:32] thread 1: 50469540 hashes, 808.16 khash/s
[2013-12-09 21:53:26] thread 0: 51850904 hashes, 833.58 khash/s
[2013-12-09 21:53:29] thread 1: 48489516 hashes, 855.40 khash/s
[2013-12-09 21:54:25] thread 1: 46821320 hashes, 834.33 khash/s
[2013-12-09 21:54:25] accepted: 1/1 (100.00%), 1668 khash/s (yay!!!)
[2013-12-09 21:54:25] thread 0: 50014552 hashes, 838.40 khash/s
[2013-12-09 21:54:41] thread 1: 13586032 hashes, 850.75 khash/s
[2013-12-09 21:54:41] accepted: 2/2 (100.00%), 1689 khash/s (yay!!!)


For best results, you should also use the above mentioned stratum+tcp protocol and adjust --threads to the number of cores in the system.