This sounds like a simple question. I will say like many other developers/architects/consultants - "It depends..."

Bottom line AJAX is bad for SEO!
For publicly facing company websites, were SEO important, stick with the server side scripting such as ASP.NET, PHP, Ruby on Rails and others.
I am not mentioning static HTML pages here since medium and big size companies most likely will have data driven web site.

If you are building Line of Service business application AJAX will only make your application better.
Do not think twice learn it well and use it.

If you absolutely have to use AJAX follow "Unobtrusive JavaScript" pattern.
AJAX is great tool when used for proper application types.

Here is my prediction -> 3 years from now Search engines will learn to understand and properly index and rank RIA/AJAX/FLASH/Silverlight/Flex/Put your faviorite client side technology here. Until then ...

AJAX and SEO: How to have an SEO Friendly AJAX website using jquery
http://www.davidpirek.com/blog.aspx?n=AJAX-and-SEO:-How-to-have-an-SEO-Friendly-AJAX-website-using-jquery

http://www.seomoz.org/crawl-test

12 More SEO Tips for 2007 http://www.seochat.com/c/a/Search-Engine-Optimization-Help/12-More-SEO-Tips-for-2007/

SEO Myths  http://www.seochat.com/c/a/Search-Engine-Optimization-Help/SEO-Myths/3/
SEO for AJAX http://www.johnon.com/270/seo-for-ajax.html
AJAX, Web 2.0 and SEO http://www.hybrid6.com/webgeek/2007/01/ajax-web-20-and-seo.php
Web 2.0 Technologies and Search Visibility http://searchenginewatch.com/showPage.html?page=3624222
Unobtrusive JavaScript http://en.wikipedia.org/wiki/Unobtrusive_JavaScript
CSS, AJAX, Web 2.0 & Search Engines http://www.seroundtable.com/archives/006889.html
Search engine optimization http://en.wikipedia.org/wiki/Search_engine_optimization

If you missed "The Business Value of SOA" presentation on InfoQ.com I highly recommend.

"In this presentation, recorded at QCon, Burton Group research director Anne Thomas Manes talks about how to make the business case for SOA.
Her talk covers explaining SOA to non-technical business people, various approaches for selling SOA to management and gaining funding for SOA investments." and much more...

http://www.infoq.com/presentations/anne-thomas-manes-business-soa

http://www.agilemodeling.com/
http://www.agiledata.org/
http://www.ambysoft.com/unifiedprocess/agileUP.html
http://www.enterpriseunifiedprocess.com/

http://www.infoq.com/minibooks/agile-patterns

"MindTouch Dream is a .NET REST framework for developing lightweight, highly decoupled web-services.  It runs on Microsoft .NET 2.0 and Novell Mono 1.2.2."
http://wiki.opengarden.org/Dream

"Spring.NET is an open source application framework that makes building enterprise .NET applications easier. Providing components based on proven design patterns that can be integrated into all tiers of your application architecture,Spring helps increase development productivity and improve application quality and performance..."
http://www.springframework.net

http://dev2dev.bea.com/alservicebus/

Nice presentation
http://udidahan.weblogs.us/2008/01/07/presentation-files-asynchronous-systems-architecture-for-the-web/

patterns & practices April 2007 DVD

http://en.wikipedia.org/wiki/Enterprise_service_bus

http://msdn2.microsoft.com/en-us/arcjournal/default.aspx

http://www.west-wind.com/presentations/howaspnetworks/howaspnetworks.asp