Take a look at the most common questions
Compilation and Protection options and features
Excel specific questions
Error messages, bugreports
This is easy. Make sure that you don't have Excel workbooks opened at this moment. Then start EXE, created by xlCompiler and run the Task Manager. If compiled application uses hidden Excel Application, you'll see EXCEL.exe process on the Processes tab. In case of the workbook compiled by our excel compiler, there should be no EXCEL.exe entry.
Also, you can run the Process Explorer application to see list of the active processes and services.
If you are using another "Excel Compiler" application, and you see EXCEL.exe - application uses Excel to display UI and evaluate values in formulas. Probably, this will lead to slow formula evaluation.