I have looked over your suggestions. The simple test form looks good and may give me useful ideas for the future, however neither seemed to meet my current needs and I am even starting to rethink some of my overall design philosophy because I'm starting to think it may have performance problems in the future.
Basically my form has two parts. There is one part that only allows users to input new records into the db through the main data data source in a repeating table. These records include their username, from the username() function and the current date.
The second part was intended to be a view only table, populated when the form was opened, that would display records from the db that had the current username and the current date (so users could see what they entered that day, before entering new records). The only way I could get this to work with my beginning Infopath knowledge was to create a secondary data source pointing to the same table as the main one and then using the conditional formatting to limit what information was displayed.
One problem that comes to mind now after reading some other posts is that it would appear that my form will read the entire contents of that table every time it is opened, so will get slower over time as more records are entered. Apparently a limitation of a secondary data source is the inability to use a WHERE clause. Also, my initial problem with the sum function was that it just summed all the records including the hidden ones. The example form with the boolean controls seems to work because the user inputs data which then causes rules to apply. However, in my example, the table is just a static, view only control that rules don't seem to work on. Are there any easy ideas out there or should I just delete this view only section of my form for performance?