Having worked with sets of comparable cards from Fusion IO and OCZ (IOXtreme and Zdrive), I can give this assessment:
Neither card met the published performance numbers. But the Fusion I/O card came closer to it's published numbers then the OCZ card in basic benchmarks making the Fusion I/O card quite a bit faster for raw throughput. Both cards were blazingly fast though pushing MBps and IOps like no tomorrow.
Real world performance suffered greatly with the Fusion I/O cards due to their software driven architecture. The CPU overhead was significant, even on a powerful multi CPU Xeon server. The OCZ cards did not have this problem.
The Price/performance ratio in real world made OCZ the winner overall. The competition was closest when excluding CPU overhead, but once you include CPU overhead the OCZ cards win hands down.
Support was highly disappointing from Fusion I/O. With OCZ you expect minimal support, but I expected something better from the "premium" Fusion I/O brand (and price point). Unfortunately, their support was no better then OCZ.
We originally evaluated the original Zdrive model which was kindof a rough implementation of the technology. If you are going to buy one now, avoid the old Zdrives...there are several problems with their design. The new R2 Zdrives have fixed these problems and are sold at basically the same price point for similar specs.
We eventually returned the Fusion I/O cards due to their ridiculous CPU penalty. We still have the OCZ cards, but have stopped using them in favor of normal SAS controllers with hot swap SSD drives. It's just not convenient to shut down a server and crack open the case just to replace a failed SSD...and SSDs do fail:) At this point, PCIe SSD cards seem better suited to high end workstation applications where it's not as big of a deal to crack open the box for maintenance.