You can download the SDK from this location: http://www.microsoft.com/downloads/details.aspx?familyid=6d94e307-67d9-41ac-b2d6-0074d6286fa9&displaylang=en .

Note (August 29, 2008): The download version and the MSDN online Library version are in synch. Both are Version 1.4 (August, 2008) and reflect changes made as part of the recent Infrastructure Update (most notably, Federated Search APIs).

Read more about the infrastructure update here on TechNet: http://technet.microsoft.com/en-us/office/sharepointserver/bb735839.aspx.

Official
SharePoint: http://blogs.msdn.com/sharepoint/
Enterprise Content Management: http://blogs.msdn.com/ecm
Forum: http://forums.microsoft.com/MSDN/default.aspx?ForumGroupID=328&SiteID=1
Discussion Groups: http://www.microsoft.com/communities/newsgroups/en-us/default.aspx?dg=microsoft.public.sharepoint.portalserver

More
SharePoint Blogs: http://www.sharepointblogs.com/
Arno Nel IW Blog: http://arnonel.com/blogs/arnonel/default.aspx
WSSDemo.com Resources: http://www.wssdemo.com/Pages/technologyresources.aspx
WSS FAQ: http://www.wssfaq.com

SharePoint Books: http://wss.asaris.de/sites/walsh/Lists/WSSv3%20FAQ/V%20Books.aspx

Workflows
http://www.developer.com/net/net/article.php/3652346
http://blogs.msdn.com/sharepoint/archive/2006/12/01/developing-workflows-in-vs-part-7-summary-and-final-thoughts.aspx

Virtual Labs
https://msevents.microsoft.com/CUI/WebCastEventDetails.aspx?EventID=1032304181&EventCategory=3&culture=en-US&CountryCode=US&flag=1

I am considering Microsoft SharePoint services to create a "Document Workspace" in a "Shared Workspace" on a server for collaborative document creation/reviewing.

Is there a sandbox server where I could try SharePoint before purchasing it?

[from RandallI - MSFT, 8/2/2007]
Try the VPC for MOSS, which is a free download here: http://www.microsoft.com/downloads/details.aspx?FamilyID=67f93dcb-ada8-4db5-a47b-df17e14b2c74&DisplayLang=en.

The download link shown above seems to be for the old version of the SDK?
----------------------------------
I've added a comment to it so that this ought now to be clear to people reading this link! (Mike Walsh)

Who can I communicate with about my improved WssTaskActivity that I would like to have adopted by the people at Microsoft in charge of the ECM Starter Kit?

I took the ECMActivities project that comes with ECM Starter Kit 1.3 and modified the WssTaskActivity class to include an OnTaskCreated workflow action. It includes the ability to call a method so that things like finding the ID value can be performed (crucial for folks who need to send out emails with hyperlinks pointing back to the SPWorkflowTask).

The lack of OnTaskCreated in the Microsoft-supplied WssTaskActivity has been the source of much grief in the SharePoint workflow developer community. Hopefully, my improved WssTaskActivity will alleviate some of that pain and suffering.

Example of user-defined method called during OnTaskCreated (with my version known as WssTaskActivityV2):

        #region OnTaskCreatedMethodV2
        /// <summary>
        /// Called by the WssTaskActivityV2 when it's TaskCreated event fires.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void OnTaskCreatedMethodV2(object sender, TaskEventArgs e)
        {
            // Pull out the goodies from the calling arguments
            WssTaskActivityV2 wssTask = sender as WssTaskActivityV2;

            // do something here

  
        } 
        #endregion