What device are you connecting? Firewire 400 is not all that slow, and eSata is a lot faster than anything else out there. Firewire seems to be fading out, even at Apple.
I don't see Apple abandoning FW anytime soon, as eSata is only good for data storage and not the other 100s of items FW is used on. I have yet to see any camcorders with eSata ports, or card readers, or still cameras, or any other multimedia device. I'm not aware of any laptops that sport eSata ports today, and they are rare on desktops as well.
That being said, it depends on what PC you have. You need to be sure and get the correct card type for your system, whether its PCI or PCI Express. I've used SIIG devices in the past, they seem to make 1394a/b cards of both bus flavors. I can understand not liking USB, its slow and too high of host CPU impact for my liking.
Yes, eSata is great for its narrow application...but it doesn't replace FW or USB at this point, and it is unlikely to as it has a different purpose.