Hey all, there has been a potential issue that's recently come to light for folks that have only applied SharePoint 2010 SP1 but not the June 2011 CU. What you will find after doing this is that the people picker will no longer work for your SAML claims users. You can still add claims via the type in control by typing in a claim value and clicking the resolve button. However, any and all names you enter via the people picker DO NOT resolve. You can get back into a good state by applying the June CU, at which point the out of the box provider for SAML will work again in the people picker. Of course, if you are using a custom claims provider for the default provider then you will not be affected by this issue.
There are a couple of other potential issues I'm still looking at right now that showed up after applying SP1 that the June CU did not fix; these are also both related to SAML authenticated sites only, for mobile devices and programmatic access. As I am able to flesh out additional details about this I will post findings on this blog as warranted.