These days, the $500-$550 mark seems an oddly expensive place for a consumer photo printer to live, but for printing your digital SLR shots larger than 8x10 or churning out those digital scrapbook pages, that's how much you've got to pony up for quality output. Not that there's a huge choice. The field consists of the relatively old, dye-ink-based Canon Pixma Pro9000 (admittedly, with some street prices that dip below $400), the not-quite-shipping pigment-based (but recently reviewed) Epson Stylus Photo R1900, and the newly announced, also pigmented, HP Photosmart Pro B8850.
You won't find a lot of differences between the B9180 and the B8850: most significant, HP dropped the Ethernet port for the cheaper model. There are some design tweaks around the control panel--no LCD text display on the B8850--but otherwise it's the exact same size and weight.
It uses the same print engine,which takes the same eight-ink/seven-color Vivera ink system (seven color because you'd never use the matte black and photo black simultaneously), and runs at the same speeds--I won't bother quoting the useless draft-mode numbers the company publishes.
The printer is slated to ship this April for $549.