To simplify this process considerably, just add a new icon to your Springboard that goes directly to about:blank. Details after the jump.
To add the new icon to your home screen, first open a new tab in Safari according to the usual method, and direct it to the url, about:blank. Then tap the more options icon (iOS 4.2) or the + icon (iOS 3.2) and select, 'Add to home'. Give your icon a name like 'New tab' or whatever you like then tap add.
In the future when you want to switch to Safari and open a URL in a new tab, just tap the 'New tab' icon, then tap the URL and X out the existing about:blank before entering in your own URL.
[crarko adds: I tested this, and it works as described. I found this even more valuable on my old, slow, iPhone 3G; and it's a good idea anytime you're using the cell connection instead of Wi-Fi.]

