HIUTIL Using 90+% CPU

You may run into this issue after upgrading to Lion or after doing some system maintenance that deletes the Help system files (same thing with Spotlight which is managed by mdworker). If that happens, just let it run until it's finished.

HIUTIL and MDWORKER CPU. Immediately after installing Lion, and over a period of a few hours, the hdutil and mdworker processes will be using up 90% to 100% of your CPU making the computer very slow. These tasks are used to update the Spotlight index and help file index. So, it’s best to wait until these programs have completed their tasks before continuing to work on the computer.

[From Apple OS X 10.7 Lion Installation Guide and Usage Tips – Including How to Create a Bootable DVD or USB Drive | ResourcesForLife.com]

Fix some Mac slowdowns

Here are some good tips for fixing slowdowns on your Mac.

Macworld | Fix Mac slowdowns

I especially like the advice given for web browsing and using Mail:

Quit and Relaunch Web browsers tend to be resource hogs, and if you visit lots of media-rich sites, this effect can increase over time. Quit and relaunch your browser occasionally (at least once a day) to speed up browsing and reduce your browser’s impact on other programs.

Over time, though, these databases can become cluttered or even corrupted, resulting in slower overall performance, among other problems. You may be able to speed up your e-mail client significantly by rebuilding the message index every few months.

Mail’s Rebuild command (Mailbox: Rebuild) works only on individual mailboxes.