Do Americans use the present perfect tense very often or is the simple past used in conversation more often?
My opinion is that Americans, whether they realize it or not, use the two tenses correctly (present perfect for incomplete action and simple past for completed action).
Let's first talk about the two tenses.
Simple past tense is made by using the past tense of a verb. Let's use the past tense of the verb "live" to make the sentence:
I lived in Canada for many years.
This sentence is saying that while I formerly lived in Canada, that has now ended.
Present perfect tense is made by adding a present tense verb (typically the verb "have") to the sentence, like this:
I have lived in Canada for many years.
This sentence says that not only have I been living in Canada for many years, I still am.
Present tenses are used to indicate incomplete actions.
In terms of how often Americans use present tenses, my opinion is that it's used whenever incomplete action is needed to be expressed - that past tense isn't used for incomplete action nor is present prefect tense used for complete action (but I'd wager they don't realize they are doing it and probably don't know the name of the tense!)
Here's more on the difference between the two tenses: