ADATA's S511 SSD offers great performance, even when compared to competing drives with higher capacities. The same SSD using the same controller, firmware & flash chips will be faster, the larger its capacity is. We see OCZ's Vertex 3 240 GB flagship, 4% faster than the ADATA S511 which is very reasonable given the S511's smaller capacity. Actually I think the S511 might be a bit faster than the Vertex 3 when 120 GB versions are pitted against each other.
In terms of pricing ADATA is asking a fair $240, which is reasonable given that ADATA has to purchase all components from external sources. However, with that pricing the drive can not make a splash on the market and draw massive attention. As always, any SSD will bring massive performance improvement over a traditional HDD - probably the best update you could pick. For optimum performance it is recommended to pair modern SATA 6 Gbps SSDs with the matching interface on the motherboard side, otherwise you'd see a real-life performance difference of around 10% which it not negligible but also not as big as what you would expect from double raw interface bandwidth.
Overall ADATA's S511 SSD is a great choice if you are in the market for a Sandforce driven SATA 6 Gbps SSD.