InfoPath 2007 essential resources
These links are from the InfoPath Team Blog
I think they are essentials
InfoPath
Improving the Performance of InfoPath 2007 Forms
https://msdn2.microsoft.com/en-us/library/bb380251.aspx
A whitepaper about performance and the InfoPath rich client. Because of differences between the client and browser-enabled forms, not everything applies to Forms Services and browser forms, but a must read nonetheless.
InfoPath Forms Services best practices
https://technet.microsoft.com/en-us/library/cc261832(TechNet.10).aspx
Microsoft Office Forms Server TechNet TechCenter
https://technet.microsoft.com/en-us/office/bb267350.aspx
InfoPath Forms Services roadmap
https://technet.microsoft.com/en-us/library/cc262885.aspx
InfoPath 2007 features that are unavailable in InfoPath Forms Services
https://office.microsoft.com/en-us/infopath/HA102105871033.aspx
Forms Server 2007 Home Page
https://office.microsoft.com/en-us/formsserver/FX100490391033.aspx
InfoPath 2007 Home Page
https://office.microsoft.com/en-us/infopath/FX100487661033.aspx
Planning and architecture for Office Forms Server 2007
https://technet.microsoft.com/en-us/library/cc303371(TechNet.10).aspx
Plan InfoPath Forms Services
https://technet.microsoft.com/en-us/library/cc262498(TechNet.10).aspx
Office Developer Center: InfoPath 2007 Resource Center
https://msdn.microsoft.com/en-us/office/aa905443.aspx
InfoPath Forms Services Architecture
https://msdn2.microsoft.com/en-us/library/ms772323.aspx
Form Development and Deployment Lifecycle
https://msdn.microsoft.com/en-us/library/ms772031.aspx
Creating InfoPath Form Templates That Work With Forms Services
https://msdn2.microsoft.com/en-gb/library/aa945450(VS.80).aspx
Support: Microsoft Help and Support: Forms Server 2007 Solution Center
https://support.microsoft.com/ph/11846
SharePoint
Plan for performance and capacity (Office SharePoint Server)
https://technet.microsoft.com/en-us/library/cc262971(TechNet.10).aspx
Plan for performance and capacity (Windows SharePoint Services)
https://technet.microsoft.com/en-us/library/cc288124(TechNet.10).aspx
White paper: Intel Performance Testing of Windows SharePoint Services (WP)
https://technet.microsoft.com/en-us/library/cc288383(TechNet.10).aspx
How to Optimize a SharePoint Server 2007 Web Content Management Site for Performance
https://msdn.microsoft.com/en-us/library/bb727371.aspx
White paper: Planning and Monitoring SQL Server Storage for Windows SharePoint Services: Performance Recommendations and Best Practices
https://technet.microsoft.com/en-us/library/cc287996(TechNet.10).aspx
ASP.NET
ASP.NET Performance
https://msdn2.microsoft.com/en-us/library/44e5wy6k.aspx
ASP.NET Session State Overview
https://msdn2.microsoft.com/en-us/library/ms178581.aspx
Developing High-Performance ASP.NET Applications
https://msdn2.microsoft.com/en-us/library/5dws599a.aspx
Monitoring ASP.NET Application Performance
https://msdn2.microsoft.com/en-us/library/3xxk09t8.aspx
SQL Server
Performance (Database Engine)
https://msdn.microsoft.com/en-us/library/bb510669(SQL.100).aspx
Monitoring (Database Engine)
https://msdn.microsoft.com/en-us/library/bb510705(SQL.100).aspx
Monitoring and Testing
Life-Cycle Performance Testing for Eliminating Last-Minute Surprises
https://msdn2.microsoft.com/en-us/library/bb905531.aspx
Server Performance and Scalability Killers
https://msdn2.microsoft.com/en-us/library/ms951773.aspx
Performance Counters in the .NET Framework
https://msdn.microsoft.com/en-us/library/w8f5kw2e.aspx
Books
Designing Forms for Microsoft Office InfoPath and Forms Services 2007 (Microsoft .NET Development Series)
By Scott Roberts and Hagen Green
Publisher: Addison-Wesley (c. 2007)
ISBN 0321410599
https://www.informit.com/store/product.aspx?isbn=0321410599
A couple of great online books from the folks in Patterns and Practices:
Improving .NET Application Performance and Scalability
https://msdn2.microsoft.com/en-us/library/ms998530.aspx
Performance Testing Guidance for Web Applications
https://msdn2.microsoft.com/en-us/library/bb924375.aspx
Blogs and Newsgroups
Pashman's InfoPath Goldmine: Tips and Tricks for Tuning Forms Services Performance
https://blogs.msdn.com/timpash/archive/2007/08/02/tips-and-tricks-for-tuning-forms-services-performance.aspx
Performance Research, Part 1: What the 80/20 Rule Tells Us about Reducing HTTP Requests
https://yuiblog.com/blog/2006/11/28/performance-research-part-1/
The first article in a series about research done by Yahoo into web page performance optimization.
Agile Testing: Performance vs. load vs. stress testing
https://agiletesting.blogspot.com/2005/02/performance-vs-load-vs-stress-testing.html
Ben Curry: Using Performance Monitor (perfmon.exe) to Monitor SharePoint Server 2007
https://mindsharpblogs.com/ben/archive/2007/02/14/1569.aspx
Ben Curry: SharePoint Server 2007 Performance Counters
https://mindsharpblogs.com/ben/archive/2008/05/07/4806.aspx
Thom Robbins .NET Weblog: InfoPath Tips and Tricks
https://blogs.msdn.com/trobbins/archive/tags/InfoPath+Tips+and+Tricks/default.aspx
Joel Oleson's Blog - SharePoint Land:
Performance & Scale
https://blogs.msdn.com/joelo/archive/tags/Performance+_2600_amp_3B00_+Scale/default.aspx
Good List of Performance Counters
https://blogs.msdn.com/joelo/archive/2007/01/16/good-list-of-performance-counters.aspx
S.Y.M. Wong-A-Ton: Enterprise Solutions
https://enterprise-solutions.swits.net/
Paul Vick - Panopticon Central: The Ten Rules of Performance
https://www.panopticoncentral.net/archive/2004/02/10/270.aspx
Technorati - infopath Blogs, Photos, Videos and more on Technorati
https://technorati.com/tag/InfoPath
Discussions in Infopath General Questions
https://www.microsoft.com/office/community/en-us/default.mspx?dg=microsoft.public.infopath&lang=en&cr=US
Use this newsgroup to communicate with the InfoPath community.
MSDN Forums: SharePoint - InfoPath Forms Services
https://forums.microsoft.com/MSDN/ShowForum.aspx?ForumID=1206&SiteID=1
This forum is another place you can ask questions about Forms Services.