Sparc migration has been the "topic de jeur" or more accurately, if less cliche, the "topic de année", with many of my customers. I am a solution engineer covering the Northwest and Canada. In this region there is a substantial installed base of Sparc systems. Many of them are getting a bit old. Virtually every user I have spoken with would like to migrate these systems to X86.
There reasons for migration are varied, but generally hit on some common themes.
Reduce the number of hardware architectures supported
Reduce the number of operating systems supported
Reduce maintenance contracts
Address licensing concerns
Move to supported ( or supported earlier) platforms
Address performance gaps
Concerns about ecosystem
In general Sparc has not kept up with Moores law. I do not mean to imply that there are not advances and some great products, but if we compare performance and price/performance of the silicon, Intel Xeon is a strong leader.
This performance gap is especially apparent for older systems. Example, if we take specint_rate_base2006 as a pseudo indicator of "general enterprise workload performance" ( i hate benchmarks, but you have to use something) we see that a single 4 socket Xeon 7560 based system delivers about the same performance a 2004 vintage 72 socket SunFire E25k Usparc IV system.
i.e. the 72 processor system that 7 years ago was sized to run your "large" ERP, decision support, or CRM systems can be replaced by a single compact blade or rack Xeon server.
Using this benchmark, Xeon beats even the latest Sparc T3-4 system socket per socket. Price performance is even better.
I get that migration is hard, and a bit scary. It may be better to stay on Sparc, than risk the companies uptime... but the risk can be minimized. There are many companies that have made the move. Xeon architecture, especially in the EX class is very robust. High availability configurations are available. Virtualization provides the lubrication for easy and dynamic scaling across machines and sizes.