Im just starting out a large enterprise level web-app and im concerned about ASP.NET 3.0 - 3.5 migration headaches later as well as VS migrations. Does it make sense to start dev on the beta and deal with some headaches pushing for a live date of Jan 1 or develop in 2005 and 2.0 and figure out what that means later?

Thanks in advance for the advice.

Personally here's how I feel:

Only you can make this decision based on factors you could never relate to us in a forum.  Budget, management decisions, project scope, etc.  I am an early adopter and started using Orcas as early as I could.  I've even put together some pretty cool things in XAML and .net 3.0 / 3.5.  I CAN tell you, that I did the same for Both visual studios 2005 (.net 2.0) and Atlas before it went to Ajax, and the transition wasnt horrible.  Mainly it involved updating the frameworks and running in debug mode for the testing methodologys that I had in place till the bugs were worked out. 

I wouldnt hesistate to start an enterprise project in 2008 right now.  And I can guarantee that the headache of updating it to the release version will be less of a headache than updating it from .net 2.0 to .net 3.0+

Great input --

 I have started in 2.0 but im not farther than some objects and a couple of forms. Easily portable and recreatable. One of the issues I'll most certainly face is the involvement of additional staff. Im concerned to make too many high level decsions without more input from .net natives (I my self come from the linux side of the fence) I'm concerned my lack of exposure is going to make it difficult for the .net dev's I'll be bringing on as the project progresses.

Thats hard to comment on, as Dev's experience and availability can vary widely from area to area.  I can tell you though, that true high class, professional developers will pick things up very fast.  I preach it like a mantra lately in my company.  We arent looking for, nor do we want to hire "programmers" .  They just dont cut it anymore.  What you're looking for is Application Developers.  The Rob Howards, Joe Stagners, Scott Gu's, Dino's of the industry that do what they do well, because they love it and excel naturally.  Obviously budget dictates how close to utopia you get in this area - but I'd shoot for 2 high end app developers before I'd hire 10 programmers.