Update: Fixed in iOS 7.
If you use Mobile Safari a lot on your iPhone or iPod touch, you may have experienced this one.
After closing all of your open sites, Mobile Safari leaves you with a blank, "Untitled" view. Now, click the home button to leave Safari. Now, relaunch Safari. Instead of just displaying that same "Untitled" view, it loads up your list of bookmarks. Now, that might be helpful to someone, but for me, I always end up tapping the "Done" button to dismiss my bookmarks, because inevitably, I already have a site or web search in mind, and it isn't in my bookmarks. Rather than tap the "Done" button every time this happens, I'd rather tap the bookmarks button on the off-chance that I do want to use my bookmarks.
Perhaps another way to fix this is to have the bookmarks display, but show not completely hide the address and search field. That might be a little too cluttered, though. Suppressing the bookmarks list is probably the better approach. It's notable that this is not the behavior for Safari for iPad, which behaves and looks more like Safari on a Mac.
If you too are annoyed by this, I do have one workaround to share for this. You can create a home screen icon for the address "about:blank" (just type that into the address bar, then use the middle toolbar button at the bottom of the screen to create a home screen icon for it). This icon will cause Safari to always launch and display a blank page.