<p>I love grids - especially the cool third party ones like Devex, C1 etc..</p>

<p>Our programmer doesn't think end users can handle them - so he always designs his forms with read-only grids (with read-only classes).  Choosing to edit an item in the grid opens up a detail form that allows editing.  </p>

<p>This app is going to be used by general business folk - not geeks.  But they are all very good Excel users - which I think is kinda 'grid' like. Should I trust my lead developer, or go with my gut which says that users like fast editing - which the grid does much better than the detail forms?  I do want to have a consistent feel to the application, so prefer not to mix it up too much.</p>

Users can totally handle grids. It's more intuitive than an edit button and a detail form.
However, is this application a multiple user application? Could the underlying data be changed by more than one user at a time?
If so, then you have some concurrency design decisions to make, and sometimes, that can be easier to solve when users can only edit one row at a time.
It smells a little fishy though, and I suspect your programmer is making convenient excuses because it's easier for him to design read-only grids in a master / detail pattern.
Stick with your gut instinct. :)