It should come as no suprise to you that Citrix thinks that VMware's software implementation of PCoIP sucks. This article explains why, allbeit on based on assumptions.

The three most amusing 'marketing' tactics about PCoIP are:

PCoIP bets on UDP as the foundational transport for graphics
One of the major design flaws in PCoIP is that it relies exclusively on UDP for deliver bitmaps. UDP is valid for some narrow use cases but PCoIP relies on it entirely. When you need a reliable transport, TCP is a much better option. The fact that PCoIP has application-layer packet reliability shows you need reliable delivery for desktop graphics. If all you are doing is playing a video, fine... but that's not what a virtual desktop is all about. You may not know this but many years ago, ICA supported a datagram-based protocol with application-layer reliability just like PCoIP. Since then, we have learned that TCP is the ideal transport for delivering desktop graphics over the network. It is also friendlier to firewall and network infrastructure. And it is cheaper to deploy as customers can leverage their existing network infrastructure.

PCoIP claims bitmap remoting is the best way to deliver graphics
Another interesting aspect of PCoIP is that the protocol is based on the idea of sending bitmaps. No wonder, since their hardware solution used as input the DVI port of the graphics card. It is interesting that VMware claim that sending bitmaps is better than sending graphic primitives. This is a half truth. While sending bitmaps make sense in some scenarios, sending graphic primitives is much more efficient in other scenarios. Think of this, what is more efficient when sending a 400x300 rectangle with black borders and white background? As a bitmap or sending a RECT command with both upper left and lower right coordinates? The key is to be smart about it and know when one scenario makes more sense than the other. That's what we call SmartRendering. Getting this right is very hard and it has taken us years of fine tuning. But a half truth is convenient because sending bitmaps is the easiest thing to do, after all, that's all most graphic remoting protocols can do.

PCoIP relies primarily on the server to do all the heavy lifting
PCoIP also focuses on the use of server resources to deliver the graphics. But you soon realize that does not get you far enough. I have spoken with countless customers asking us to solve their scalability issues with playing Flash multimedia. I'm sure VMware have shown some YouTube videos to get people excited but you have to look at the CPU and bandwidth consumption. The Flash player uses up lots of CPU, so if your only available solution is server-side rendering then you are going to need a lot of servers. Customers need solutions that scale, are cost effective and leverage their computing resources in the data center and also on the user device. PCoIP fails to do this because it is an incomplete protocol.

Source: http://community.citrix.com/pages/viewpage.action?pageId=100302964