I might have found the difference. The 290 has a 200 gig 5400 rpm HDD while the 270 only has a 160gig 4200 rpm drive. Is that the only difference? As far as I can tell. Is it worth it? maybe. It depends on how important file access time is to you. The 5400 rpm drive will be better than the other one, a 7200 rpm drive would be best.
For a better comparison of the two look at these specs:AR270AR290