Has it been mentioned that spoken English is almost always different than written English?

There are terms and phrases that are used in colloquial speech, yet are never used in writing. Also, as others have stated, there are written phrases that are in common usage that are grammatically incorrect, yet are replaced by their incorrect, less obfuscated-sounding counterparts.

There are some things that I believe that should remain consistent in our language, yet, as language is an evolution, people need to recognize that things do change, and will continue to change, for as long as humans exist. Thus, this should not really be a point of contention.

That said, there is nothing fundamentally wrong with using slang and/or colloquial forms in place something that could possibly alienate you by making you appear as if you stepped out of the 1600s. I will not knock anyone who chooses to say "I am smarter than her" in place of "I am smarter than she." In fact, I'm going to encourage it, as long as you are conscientious of the correct form.

Lastly, if it makes things simpler for both the writer and the reader to understand, then one may opt to say, "She is smarter than I am," rather than saying, "She is smarter than I." I'm not advocating the dumbing down of the language, but if you have to find a medium between sounding silly and being grammatically correct, that is it.