Whilst Dot Net has largely shielded us from 32-bit v 64-bit issues, it is good to read an article like the one on Code Project about "A Collection of Examples of 64-bit Errors in Real Programs"
Have a read of it at http://www.codeproject.com/KB/cpp/Examples-64-bit-Errors.aspx, you will appreciate what Microsoft have done for us application developers with Dot Net.