I wish the default for an Advanced Search function was to Search a Single Content Type, namely Posts. Partly because that's where I think most people will want to search most of the time, and partly because the result set returned when you Search Multiple Content Types with only Posts checked never contains as many posts as when you search a Single Content Type specifying Posts.
As an example, try this:
Using the Advanced Search function, on the Search Multiple Content Type tab, tick the Posts checkbox and search for those with 2012 in the title. At the time I write this, that search will return 17 results with a line at the bottom that says "Results 1 to 17 of 18" but no way to access the 18th result.
Running that same search from the Search Multiple Content Type tab with the All Types checkbox ticked returns the same result.
Now go to the Search Single Content Type tab, and search Posts with 2012 in the title. At the time of this writing, this search returned 56 results, on three pages, all accessible.