I purchased all the Honda factory interior trim pieces and installed them myself. They adhere with double-sided taped and so far seem quite secure. It really does add a finishing touch to the interior, especially the pieces for the door. Everyone that saw them at the recent Huntington Beach get-together thought they looked great.
Although they may seem pricey, I thought it was worth it. If the $$$ is an issue, check out eBay and take at look at the aluminum interior trim kit that someone is offering there. It's only $150 and has like 20-something (!) pieces to the kit.