Details: One of the new features / enhancements in SharePoint 2010 is the support for large lists ( upto 50million ) and also supports to set limits on top of these large lists. Consider the list has 'X' number of rows ( think of a big number ) and say user is querying 'Y' records of it and 'Y' is very near to 'X'. In that case, you can restrict the rows returned in order to prevent large queries. Though you can set it using the UI as show below, you can override it using the code also.
Code: To enable or disable throttling, use the property as show below.
list.EnableThrottling = false;
To access from UI, go to CA > Application Management > Manage Web Applications > "Select Web Application" > General Settings > Resource Throttling.
One important factor to consider here is while migrating from MOSS 2007 to SPS 2010, beware that throttling settings might effect your existing functionality since such new feature doesnt exist in MOSS.