It is very easy to add POI in S&T. I have done it very often myself. When browsing POI web site, just search for excel file (.xls) or text files (comma separated text file).
Then in S&T, open the .est file you want to add your new POI (like a list of walmart, campground, and so on) to it. In the Data menu, choose import data wizard. Then you have to choose the file type you want to import (usually excel, text, ...). Then you may choose the country region (other if multi country).
Now you have a chance to format the data with column to separate them: name, address, latitude, longitude and so on. This step can go gracefully or not. It depends how good is the source file. If the first row of the data is the column headings in the source file, you may select this as well. If the first row has not column headings or the headings are not recognized by S&T, you will have to edit the data type for each column yourself (minimum needed is Name, Latitude, Longitude). Once done, you click finish and it will import all the records and validate them. You will see for a while how many records have been accepted and how many have been refused (you may check this carefully later by doing properties on the new pushpin dataset, under the matching tab, you should get 0 for number unmatched, if a great number did not match, the source file is not good, you may have to modify it, see below...).
This will create a new pushpins dataset that has the name of the file you imported as the dataset name. At this point, i am usually changing the default pushpins associated with the dataset (like use a tent for campground and so on. You may also import some icon bitmap that are generally available with the POI source file).
To change the pushpin icon, open the legend and overview pane. Then select the new pushpins dataset imported (that is matching the file name), right click properties, and choose a new icon under general tab, symbol.
A good place to start for POI:
http://www.poi-factory.com/
Important:
1- If the import operation went very bad, sometimes the source file format is not good for S&T. It could usually being repaired easily yourself by opening the excel or the text file, and taking care to split every information carefully in column (for a text file a column is delimited by a comma), with 1 information category in each column. Take care if one information is missing in a row to let a blank in this column category so the data import goes well later...
2- If you want to have these POI to many of your route .est files, do the same to an empty .est file and save it as a template to start your new routes later, so they will have all the POI...
Example of multiple imported POI files:
http://www.laptopgpsworld.com/1063-does-streets-trips-need-legend-overview-pane#post7051
Enjoy