Good question - for on-screen development, generally it's best to use 72 or 96 dpi, as monitors don't display higher resolutions that that.
275 dpi will not improve on-screen quality, it will simply make the file sizes much larger than they need to be.
<ultra-quick resolution tutorial>
Say you have a 100dpi image that is 100 pixels across. On your screen, that image will take up 1 horizontal inch of screen size (on a theoretical monitor that displays stuff at 100dpi). Same with print - it will be 1 inch wide on a page.
If you have a 200dpi image that is 100 pixels across, you're fitting twice as much information into that image, which will look better on paper, because there's 200 dots in that inch instead of 100.
But on screen, it won't look any better, and you'll be storing more information than the 100dpi image. On our theoretical monitor that displays 100dpi, there's no point to using more than that.
</ultra-quick resolution tutorial>
This applies for whatever screen resolution you're developing for - the picture will simply take up less screen space on higher resolutions. For example, a 100 pixel wide image will take up 1/8 of the space in 800X600, but only ~1/10th of the screen space in 1024x768.
So after all that, stick with 72 or 96 dpi for images intended for screen display.