I usually get at least 1 email a month asking me some form of the below questions about Virtual Earth / Bing Maps for Enterprise Licensing. So, I’ve decided to post some information on the topic.
I’m not a Bing Maps for Enterprise (formerly  Virtual Earth) Reseller, nor do I work for Microsoft or represent Microsoft in any way; so the following tips/faq are my own opinion and do not represent Microsoft in any way. For official answers, please contact Microsoft directly and refer to the “Microsoft Virtual Earth Platform API Terms of Use.”
Email all licensing questions directly to Microsoft at maplic@microsoft.com
I encourage you to read through the official “Microsoft Virtual Eearth Platform API Terms of Use”. You can also find more information on the “Microsoft Bing Maps for Enterprise – Licensing And Pricing Options” page.
I am not responsible for any actions you take based on the tips/faq provided below. The below is provided for informational purposes only and is not provided as legal advise. It is always recommended you consult an attorney.
Now that I have the disclaimer out of the way…
Q: Do I need to Pay / License Bing Maps for Enterprise to use the JavaScript Map Control and/or Web Services within my Website / Application?
A: There are really two separate answers: 

1) Non-Commercial Use: No, If you are developing or hosting an online application that uses the service to display results for N**on-Commercial Use, **you do not need to purchase a license agreement from Microsoft. 

2) Commercial  or Government Use: Yes, If you are developing or hosting an online application that uses the service to display results for Commercial or Government Use, then you are required to purchase a license agreement from Microsoft. However, you are allowed to use the service for a 90 day evaluation period before you are required to purchase a license agreement.
There are some additional restrictions for using the Service for Non-Commercial use and within the 90 day evaluation period; these restrictions are outlined within the official “Microsoft Virtual Earth Platform API Terms of Use.”
Q: Can I use the Silverlight Virtual Earth Control CTP within a Website / Application?
A: **Officially, the answer is **No. Since the current release of the Silverlight Virtual Earth Control is a Community Technology Preview (CTP) it is not licensed for use in any Production environments.  Also, there is no support provided for any bugs that you may encounter while using it.

However, you can use the Silverlight Virtual Earth Control CTP for Development and Testing purposes.
Q: Can I use Bing Maps (Virtual Earth) within a Windows Forms or WPF Desktop Application?
A: As far as Licensing, you’ll need to contact Microsoft. The “Microsoft Virtual Earth Platform API Terms of Use” doesn’t really cover this specific usage scenario.

Microsoft doesn’t have a Window Forms or WPF control that you can just drag onto a Window, but you could access the Web Service from your application or display the JavaScript Map Control within an embedded WebBrowser control.
Q: Can I use the Virtual Earth Server Control that’s part of the Windows Live Tools CTP within a Website / Application?
A: No, Since the Windows Live Tools is a Community Technology Preview (CTP) it is not licensed for use in any Production environments, and thus all the controls within the Windows Live Tools CTP are licensed the same.

Also, the Virtual Earth Server Control within the latest release of the Windows Live Tools CTP is buggy and only partially implemented.
If you are looking for an ASP.NET AJAX Bing Maps (Virtual Earth) Server Control that you CAN use in Production and is Fully Supported, then I encourage you to check out the Web.Maps.VE product by Simplovation.