The existing contact Activity lookups only filter by "Since Date" which is very limiting. If I want to find all the contact records that have changed in some way last calendar month, or the month before that, I can't do it by this method.
Same problem with the data chart dashboards.
I therefore suggest that all "Since Dates" in ACT! are replaced with tthe "standard" ACT! date range dialogue i.e. This week, last week (etc) plus custom date range.