The iLiad makes heavy use of icons. Unfortunately, when creating the icons the designers obviously failed to talk to anyone with a background in human-computer interaction, and many of the icons are totally incomprehensible. After a bit of trial-and-error (mainly error), you get used to them, but you'll never really grow to like them.
The PDF reader feels half-finished, a feeling that's amplified when you install the community version. Since iPDF is based on Xpdf, which is licensed under the GNU General Public License version 2, iRex was required to release the code for its changes, and the community has extended it with various features such as the ability to hide the buttons at the bottom and make the page take up the whole screen. Both versions have the ability to annotate PDFs. Your doodles are stored in a separate file in something a lot like a NeXT/Apple bundle, and can be merged with the PDF later using third-party tools.
The biggest problem with the iLiad software is the complete lack of power management. When reading a page, the power drain ought to be close to zero. No power is used to keep the image on the screen, and the CPU is idle. The community-developed version of the PDF reader includes CPU power-management features, scaling the speed back to 200 or 100 MHz. Ideally, the device would enter a full suspend-to-flash mode after half an hour of inactivity, dropping power usage to nothing and not losing any state, but this doesn't happen. You're lucky to get more than a day of use between charges.