I have a Mushkin Enhanced Chronos 120GB SSD (http://www.mushkin.com/Digital-Storage/SSDs/MKNSSDCR120GB.aspx). Its performance is rated as:
Read Speed: up to 550MB/sec
Write Speed: up to 515MB/sec
Interface Type: SATA 3.0 (6Gb/s)
IOPS: 90,000 (4K random write, 4K aligned)
My performance however is much lower.
Screenshots from HD Tune Pro 5.00:
I am however using this on a SATA2 port, while it is a SATA3 SSD.
The other hardware:
Motherboard: Gigabyte ga-ma790xt-ud4p (http://www.gigabyte.us/products/product-page.aspx?pid=3010#ov) (latest BIOS (F8))
Processor: AMD Phenom II x4 955 BE
RAM: 16GB (4x4) Corsair Vengeance (http://www.corsair.com/vengeance-8gb-dual-channel-ddr3-memory-kit-cmz8gx3m2a1600c9.html
Graphics card: ATI Radeon HD4890 1GB (http://www.amd.com/us/products/desktop/graphics/ati-radeon-hd-4000/hd-4890/pages/ati-radeon-hd-4890-overview.aspx
It has always been this slow, I haven't seen the performance go down since I started using it.
Here's a screenshot from ATTO. It looks a bit better then HD Tune Pro.
After enabling AHCI: