I'm guessing its to late to turn back now... I'm all for it, only because there has been such a drive with AJAX how could you avoid the desire to use it.
Yes there are some issues but I'm not so worried the SEO issues will be around for long. I might suggest having a non-AJAX link area to some key content scattered thoughout the pages just to help balance and give you some anchors perhaps.
I'll also suggest reading this article she makes a couple nice points...