Working with SharePoint 2010 is really a joy, you stumble upon great things all the time. The API has not had any revolutionary changes to be backwards compatible; but small changes here and there, both publically visible and internally, really makes the API better than before.
To get the Content Type Id of an SPListItem you had to first get the SPContentType from the SPListItem.ContentType and then get the Id of the content type. This method was one marked as internal in version 12, but is now marked 14. It’s those little things. There are actually a lot of previously internal properties and methods that now are public, for example the CanBeDisplayedInEditForm property on the SPField class.
Last year I wrote a post about this one and now it’s there. No need to encapsulate your code with try-catch blocks when trying to get a list using it’s name. TryGetList will return null if the list does not exist. Thank you guys, up there in Redmond!
SPWebPartManager disposes the SPWeb object
One change that is really great. When using the SPWebPartManager or the SPLimitedWebPartManager you previously had to manually dispose the SPWeb object before disposing the Web Part manager, now that’s done when disposing the SPWebPartManager or the SPLimitedWebPartManager. This will save a lot of people a lot of memory leaks.
This is an interesting one, using this method you can find out which sites and lists a specific field is used. The method returns a collection of SPFieldTemplateUsage objects, which contains Guids of the list and site Id’s. One thing that also is interesting with this one is the usage of the templated ICollection instead of an array or custom collection.
There are of course a lot more, but these four I did find during my excavations this weekend. Have you found any favorite change except the obvious ones?