5 years ago when they were trying to sell this thing for over $200 it wasn't worth it, but at $90 and after reading that they fixed issues preventing it from competing with normal network cards I thought I would give it a try.
All I really have to say about it is that I really don't notice a difference. I still keep it in because if I take it out and experience lag I always start thinking I shouldn't have taken it out, but I'll admit that this is probably nothing but a placebo.
Back in the day offloading networking to a separate piece of hardware was a great idea but nowadays when pretty much every CPU is capable of running 4 or more threads simultaneously, this is no longer an issue.
The only other reason to get it would be the application bandwidth throttling in the network manager, but the drivers are a resource hog and I don't really use them. If you think you would then go for it, otherwise save your money.
Intel Core i7-875K, Asus P7P55D-E Pro, Win 7 Home Premium
MSI GTX 560 Ti OC, Mushkin 2x2GB DDR3-1333, Corsair TX650
Cooler Master Hyper 212+, Logitech Z-2300, ASUS Xonar DX
Samsung Spinpoint F3 1TB, Dell Ultrasharp U2410, Antec P183