Mobile Safari on the iPhone does an amazing job displaying web pages. However, I find that in the context of viewing some web pages on the go, that this view isn't necessarily the best way to read some pages. For example, even though the iPhone interface is awesome, I don't really want to waste time zooming and messing with a page to read the actual content. I'd rather just load up a page, read my content, and move on. (Of course, the best solution would be if web designers designed alternate "iPhone-optimized" views that would look great on the iPhone, but only a few mainstream sites do this as of the time of this post.)
I discovered back in my Treo days that Google has a page that translates web pages to "mobile-friendly" versions. I find that loading pages using this URL reduces page load time, and makes them easier to read on the iPhone. So, I created a bookmarklet that allows you to take the current page in Mobile Safari and run it through the Google page to display a mobile optimized version of the site.
This is really helpful.