the Delete/Backspace key

No and No. I've never seen a software keyboard get stuck but it sounds as if yours is. First I'd try a reset by pressing the home and sleep buttons until you see the Apple logo, ignoring the slider. Takes about 5-10 secs of button holding and you won't lose any data or settings. If that doesn't work, try a restore... see page 141 of the manual... http://manuals.info.apple.com/enUS/iPhone_UserGuide.pdf

i think i may have experienced this before...def. not frequently.

what i think is happening is when you go to delete, there may be some sort of delay or lag. and so you're tapping delete. it doesnt seem to be deleting so you tape a bunch of times. the phone actually registers all those taps and deletes as many characters as taps, or similarly, continues to delete for the duration of how long you've held the delete button.

unfortunately my only advice at this moment is to delete slowly...and patiently.

What version of the iPhone OS are you running? This was a bug under 2.0 and 2.0.1 (one that I experienced), and some users reported it in 2.1, but I have not had it happen or heard of it happening in 2.2 or the current version, 2.2.1.

I assume you know that the backspace key has a built-in function of deleting entire words if you hold it down and doing so faster the longer you hold it (not 100% sure about that last part, but that's how it appears to work). This can indeed "run away" if there is lag in the system because a regular press gets delayed, then the next one gets caught in the pipe and it "thinks" you're holding it down.

-dan