Warren Ponder, a Senior Technical Marketing Engineer at VMware, is one of these individuals that also (not surprisingly - VMware and Citrix have been exchanging "emotions" quite frequently recently) feels that Calista poses a threat to ICA (to say the least). In his blog, Warren also discusses the consequence of another action by Microsoft that got relatively little attention: the publication of the specifications of a LOT of Windows client and server protocols . I say LOT because it's over 30,000 pages of information. One of the protocols that is also covered is RDP. Everything you ever wanted to know (or did not want to know) is now publicly available.

Warren's view of this information is that it is inevitable that RDP will be enhanced so much in the near future that ICA will loose it's edge in the presentation protocol market. Warren even suggests that Citrix will probably have no choice but to open up the specification of ICA as well. While I feel that this might be a bit of a premature prediction to make, I do agree that ICA will get some fierce competition in the near future, more than they have had so far.

In order to keep the edge that ICA currently has, Citrix needs to keep adding features to ICA that really make a difference. One problem that I could foresee is that Citrix is kind of the victim of their own success. ICA is already so advanced that other additions would probably fall in the category nice-to-have as opposed to must-have. I've seen this happen in Presentation Server as well. Let me give an example: when Citrix introduced 16 bit color as opposed to 256 color this was a must-have. When Citrix introduced 256 bit encryption as opposed to-whatever-number-it was-earlier this was something that would fall in the nice-to-have-category. 

Anyway, exiting times lie ahead. Whatever happens, I'm sure this will be a win-win for users of presentation protocols.