From SharePoint 2010 Microsoft promises us, that they now are able to handle large list – namely because they now have implemented “Query trottling” that prohibits (limits?) queries, that return too many items. So you think to yourself: Wow – that’s nice! Now I can implement applications that supports large amounts of data; You start implementing your solution; You test it on your development box (where you probably like me are running as Farm Admin, so you can install your new application) – you even do a test with at least 5001 items in a list (over your throttle limit), and everything seems to be working. Then you hand it over to the customer, for them to install, and it works for a couple of days – but as soon as the customer inserts item number 5001, everything stops to work.