Yes, it happened to me. Yesterday morning, the front page of my site was marred by two screens' worth of links to porn sites. I couldn't tell where it came from, which file it was in. I contacted my new WP guru, who had responded to a question of mine in the wordpress.org forum, and she and her database wizard are in the process of fixing the site. She thinks the hack actually happened in July, but was activated only yesterday. I had already installed WP 2.8.4 the day before, but I guess since the hack was in place while I was using 2.7.1, it was able to wreak havoc.
So, please, please go ahead and upgrade to 2.8.4 ASAP! I will post more as I find out more, and also about ways to "harden" the site against future attacks. I guess one problem with open-source platforms like WP is that the hackers have an easy time writing malicious code to get into it.