No two choices should have the same ID

In any case avoid create different fields with the same Guid OR - and this is important - the same internal name.

This is never checked by the solution packaging mechanism or while adding or installing the solution to the solution store. The errormessage "No two choices should have the same ID" occurs, if you for e.g. try to add an existing field to a sharepoint list.

Be sure to check this from time to time during development-process and before setup your solution to the production server. If the system is up and running, it's very difficult to do changes here...

Central administration 2010: Solution store, where did you go?

With no applications- or operations-tab no more, SharePoint's Central Administration looks a little more cleaned up... and messy too. Where the heck did the solutions store from Operations > Solution Management go to? In CA 2010 you'll find it in System Settings > Manage farm solutions or Manage user solutions (for sandboxed solutions):

Alternatively you can get a list of installed farm solutions by using the SharePoint Management Shell Commandlet Get-SPSolution or for user solutions by Get-SPUserSolution.