I guess it depends on your perspective, but for me (as a dev) sharing XAML has been a great experience. I've worked with designers who didn't use Blend but it's been easy to copy and paste their Illustrator created resources into my projects. Usually I'll ask them to install this plugin http://www.mikeswanson.com/XAMLExport/ and send me the results of their export. I'd recommend using Silverlight 3 for the merged resources feature - then you can keep each resource they give you in a separate file and merge them into App.xaml so they're available throughout the application (helps to keep updates to resources clean).
Aside from that make sure you hook up event handlers in code instead of XAML and use MVVM with Silverlight binding as others suggest. One part of MVVM is currently missing from Silverlight - the ability for the UI to fire off commands that the VM can listen to. Check out Nikhil Kothari's Silverlight FX project (sorry no link, looks down ATM) for my favoriate solution to this problem or use the Prism framework from Microsoft at http://www.codeplex.com/CompositeWPF for a more heavy-weight implementation (with more features, of course). I use Prism at work and generally like it. Of course you can take the easy way out and just call methods on your VM from the Xaml code behind.
You might want to consider moving to Team Foundation System for source control - that coupled with Blend 3 will allow your designers to check out / check in their work to source control, which is a huge plus IMO. For learning blend check out the "Principles of design" series here http://team.silverlight.net/ and also Kirupa's work here http://www.kirupa.com/blend_silverlight/index.htm . Enjoy your simplified development life ;)