As opposed to the information in KB897567 Rev. 3.0 with the short name "Known issues that occur with public instant messaging after you install Office Live Communications Server Service Pack 1" EASI domains are supported by now (Actually by October 11th). Earlier only domains like hotmail.com, messengeruser.com etc. were supported with MSN Messenger connectivity but now domains/addresses like email@example.com are also fully supported (I've just tested it together with a Microsoft contact of mine).
You will have to add EASI passports using a special syntax of user(easidomain.com)@msn.com e.g. the EASI passport firstname.lastname@example.org would translate to msnuser(inceptio.dk)@msn.com.
If you are considering using PIC then there are many interesting quirks documented in the KB article. One of them is that the MPOP functionality doesn’t work together with MSN/Yahoo/AOL (MPOP is Multiple Points Of Presence where Office Communicator 2005 supports being logged on to several devices at the same time - including the upcoming Microsoft Office Communicator Mobile).
Furthermore, if you're using multiple domains in LCS then be sure to get a public certificate from a provider that supports Subject Alternative Names (Source).