Dennis Clark makes a comment on his blog regarding the difference between the Sun and IBM grid offerings. Sun offers grid capabilities for $1 per CPU per hour. IBM on the other hand requires you to pay $49,000 to get started. Sounds like a big difference. However, after doing a quick back of the envelope calculation it looks like it would cost around $8760 to use one CPU on the Sun grid for an entire year. So for a typical dual CPU Intel P4 Xeon server you're looking at $17520 per year. That implies 2-3 servers worth of CPU power will cost you about $50k for a year with Sun's solution.
Now, you may say the whole point is not to have to use the server for an entire year but instead to use what you need. That's true. The IBM solution seems at first glance to be geared more towards people who want to purchase the hardware outright and let IBM manage the servers in the IBM data center. I could be wrong about this... I'll need to do some additional research to find out.