Two major differences:
1. 9 speed triple left-hand / front derailleur shifter has 9 index positions which essentially replicates indexed bar-end or downtube shifter trim positions.
2. Completely different interface with the hand and fingers relative to grip and shifting. Having small hands, I found the Ergo's to be a much better fit.
With the introduction of the Shimagnolo (since discontinued) and
J-Tek shiftmates, you can now use Campy's Ergo levers with Shimano deraileurs and cassettes, so a complete hardware change isn't required to make the change anymore so that making the switch to bar-ends. Of course, the conversion cost isn't insignificant. The only thing about the J-Tek is that you do need to occassionally re-set the pulley to it's 1:00pm clock position to keep shifting as good as it can be.
This article is a bit dated, noting that both Campy & Shimano have continued to make improvements and refinements in their shifters. However, many of the major differences associated with the "fit" of the different shifters still applies:
http://www.thetandemlink.com/stivsergo.html