After using Wordpress for around 5 months, I finally made the change because of the high CPU usage from wordpress.
Serendipity, Drupal or wait for next version of Wordpress to come out are the 3 choices I'm facing. There is no harm by trying the first two, so I ported my post in both Serendipity and Drupal.
The decision was hard, but I finally made my choice by selecting Serendipity for these reasons.
1. I don't see any report of Serendipity ever uses 100% CPU
2. Serendipity have a non-php-script-based template system(so does Drupal)
3. Serendipity are made for blogs, unlike Drupal, which is more toward a portal system.
4. I can't wait two days for wordpress 2.2 to come out!

I tired Serendipity first, just to see if I would like it or not. Serendipity compare to Wordpress, it's ease of use drop down to the dump.
Use the defult theme browsing the admin panel is as painful as browing the Drupal admin panel, because the UI is mind blowing(not in a good way). Wordpress, having dash board with huge buttons, clearly wins out in this.

Few seconds though exploring in the plugins, I found a plugin that implement one of the cutest feature--download plugins directly from the Serendipity respitory. But sadly it isn't working that well. I tried to download GeSHi plugin and it paused at inno.php for like 5 minute until I finally can't wait and download it from it's official site directly.

Anyway, I have to use the next week(mon-fri) fix all the problem from porting things from wordpress to Serendipity.