Why I don't think XPages will make a difference in turning the tide...
Disclaimer up front... There are generalizations in here, because actual seat counts and win/loss claims are hard to decipher from press and vendor spin. Your mileage may (and probably will) vary from what I'm about to write...
I know that many have looked at XPages as being a key factor in turning the Domino platform into a first-class application server. And I agree... it is a positive move in the right direction in terms of what Domino can do now both on the web and on the client via XPages.
But overall, I have no confidence that it will make any difference in stemming the tide of what appears by all accounts to be a continual slide in lost Lotus accounts. The latest loss is the GSA decision, and nearly all the pundits and accounts make it sound like Google and Microsoft were the only two competitors for the business. The loss of the account by Lotus is portrayed as a done deal, a foregone conclusion. The analysis is how Microsoft is going to counter Google's move into government accounts, with little being said about how Lotus might factor into any decision.
Mail and application migrations are two entirely different things, but it's been my observation that the same path seems to occur when a Lotus account is lost. Mail migration takes place at some pace. In some areas it's fast with a total cutover, and in other locations it's a long, drawn-out affair. But simultaneously, the decision is made to scale back or freeze additional Notes development while migration plans are figured out. There are obvious horror stories on application migrations, and few seem to get totally off of all Notes applications very easily, but there seems to be one constant factor... no one is committing resources to enhance and expand their Notes portfolio if they've migrated to another email platform.
Email and applications are intricately linked when it comes to using Domino, and if you lose the email battle, you lose the applications battle.
I don't see that many (any?) people are buying Domino as strictly an application platform, nor is IBM pushing it as such. Because of this, it seems that any new technologies like XPages are at the mercy of whether an account chooses to stay with Notes email. If that's tossed, XPages won't save Domino in an organization looking to cut back on their IT spending.
I think XPages is an important skill to learn if you're in a Domino environment that is committed to that platform. But I see more and more organizations that are questioning that commitment, and are making the move to either premise or cloud email from Google or Microsoft. And when that happens, Domino apps are in a precarious (and often deadly) position, regardless of whether XPages exist or not.