>as a table or "table" (whatever), but if you don't it's a... what? A collection of objects with one property per field? Or a collection of records, where each record is a collection of field objects? How do you apply something to a column (as in "replace all field4 with [goodbye]"), or how do you relate the records?

A DataSet is a collection of DataTables and info. about any relationships you might want to set up between them. A DataTable is a collection of Row objects. You can apply things to all columns by looping through the rows in a foreach and setting the value. Or you could use LINQ to apply the values.

DataTable table = ds.Tables[0];
table.AsEnumerable().Where(currentRow => true).ToList().ForEach(item => item.SetField("field4", "goodbye"));

You don't really need the Where clause, I just included it there to show that you can do some evaluting to filter the result. If that's a bit wordy it's easy to add extension methods to shorten things up (ex. add something like a Replace() method on a DataTable that lets you pass in the filter, field, and values).