One of the biggest problems with SharePoint 2007 development is that all of its solutions run as full trust… SharePoint Pro Connections just published an article I wrote which discusses one of the new features in SharePoint 2010, Sandboxed Solutions. Sandboxed solutions enable you to run solutions in SharePoint in a security sandbox. This allows administrators to trust the code that developers write. And it allows developers to more rapidly develop and deploy solutions without fear of taking down the entire farm. Sandboxed solutions are the default way to create SharePoint business applications for SharePoint on premise and SharePoint Online.
Read my entire article here: SharePoint 2010's Sandboxed Solutions