I have nothing but great things to say about the Promise line. Their support is top notch, prices competitive, and the performance is great. Their consumer line is in a sweet spot of value from where I sit.
I like that it's a true raid and not a proprietary storage format like Drobo. Every time I look to recommend a DIY / kit storage, their price is competitive to bare kits without all the hassle of drivers, guessing which case is nice, which controller is best, etc...
I also like that Apple selected them for their enterprise storage as well as sell their product in the Apple web and Retail stores, so you know the companies are working together to make sure everything works well when new hardware and software comes out.