>This seems like alot of work, and must be really slow when large datasets are returned. (100K records for example).

What tier are you designing that requires 100,000 records? Usually, business objects and user interface objects don't deal with 100k records from the same entity. There are of course, exceptions to this, in which case, you would need an exceptional data format/transport solution. In the most typical of business logic, however, its less of an issue.