The stupid forum engine didn't like the title I gave this review last time, so here's a second try. I just picked up an 8450 less than a week ago, and am generally extremely impressed with it (it replaced a much more expensive Stylus Photo 2200 that broke). The best feature, as far as I'm concerned, is that it produces 8x10 glossy prints with custom lab quality and absolutely no profiling hassles. Once I figured out the best workflow (let Photoshop handle the profile, use HPs provided profile for Premium Plus glossy-tricolor/photo/gray ink), this printer hits right on the (calibrated) monitor rendition every time! It has a large enough gamut that it is capable of printing AdobeRGB (a first for an inkjet?), and I actually like its native colorspace better-it's a touch warmer than AdobeRGB. I turn on proof colors in Photoshop, set it to proof the printer's colorspace (with "preserve color numbers" off), and I get a near-perfect match with the monitor, except that the printer, having the advantage of much higher resolution, adds detail and color depth. No need to fool around with profiling the printer-exactly the opposite of the Stylus Photo 2200, which never liked to match monitors, so it required expensive custom profiles or lots of test prints.
In addition to the near-perfect colors, the resolution of this printer is very high (I can't tell if it is actually higher than the Stylus Photo 2200, which was also a very detailed printer). A friend and I are learning large format photography together, and I've sent the 8450 a bunch of scans from 4x5 inch Velvia. The resolution of the printer is so high that it is easy to tell the difference (upon fairly close inspection) between a large format scan and a good 6 MP digital file (Nikon D70 at ISO 200, always shoot NEF raw). The D70 native resolution at 8x12 is about 250 dpi, so it should be enough for a good print. The 4x5 scan is a 600 dpi file (and I actually have to downsize it substantially in Photoshop to get it to "only" 600 dpi at 8x10. The D70 is a very nice 6 MP DSLR, which is certainly capable of a high quality 8x12 print, but the Photosmart brings out the extra detail in the big film.
The one disadvantage is that it is expensive to operate-its favorite beverage is large quantities of gray ink. The consumption of the other two cartridges is actually quite reasonable. I only got 16 prints (all 8x10-8x11ish on Premium Plus Glossy) out of my first gray cartridge (supplied with the printer), which is supposedly a full one. HP sometimes supplies half full "starter" cartridges with printers,and I suspect that the initial gray cartridge could be a starter (although it is not marked as such either on the cartridge or the printer box) because I've made four prints off the new one and the front-panel ink indicator hasn't budged. The tricolor is right around 50% after 20 prints, and the photo cartridge is still above 75%. I'm guessing that if that first gray cartridge was full, I'll get an average of 20 prints off a gray cartridge (there were several dark prints that really chewed up the gray ink in that first batch), 40 from the tricolor, and some indeterminate but large (100?) number from the photo cartridge. That adds up to roughly $2.00 in ink per 8x10 print. Add 85 cents for paper, and it is nearly $3.00 to run an 8x10.
The tradeoff for the high running cost is that it nails the print the first time, and gives custom lab quality. With good Photoshop work, it sure beats any minilab, and actually outperformed a professional LightJet on the same print. LightJet prints are $6.00 to $15.00 per 8x10. This is certainly the highest quality output device I've ever used, and arguably the best I've seen results from.
I really haven't gotten into the fancy features-I just drive it off my Mac printing directly from Photoshop CS. It's hooked up via Ethernet, which is really useful when sending it hundreds of megabytes of scanned 4x5.
What I'd really love to see is a "DesignJet 170"-a DesignJet 130 with these eight inks. The running cost would go down drastically with those gray inks in big cartridges. The 24 inch carriage would provide a ton of flexibility in terms of print sizes. Judging by the aggressive pricing of the 8450, the DesignJet 130 and the 130's consumables, Epson should be very afraid that HP will do this. I'd guess that it would be a $1000-$1200 printer (just a bit cheaper than the 130, because the prices on these things always go down each generation) that would outcompete the $3000 Stylus Pro 7600. The 130 already mildly outperforms the 7600, and the extra gray inks (I believe the 130 uses six of the eight inks from the 8450) would improve performance even more. The "DesignJet 70" 13 inch version could kill off the Stylus 1280 and 2200 with higher print quality and MUCH lower running costs, not to mention greater paper flexibility. Supposedly, these new-generation dye inks have similar longevity to UltraChrome pigments, so Epson's one big advantage is gone. Of course, you do have to use the right paper to get the longevity, but that's equally true of UltraChrome (to avoid bronzing).

-dan