There's been a lot of discussion about Market not showing apps, and changing dpi to fix that. Also, many of us like to change the dpi to make the screen icon size (bigger or smaller) to make it easier to read/show more content. I used to use 174 (I think) for our Nooks because I had read it was optimal for that device and since my wife has vision problems, the slightly larger display worked better. When I read about Market issues and changed back to 160, within a few hours I noticed a lot more apps had updates in Market.
I ran across this thread for the HP Touchpad w/ CM7/CM9: [REL] Market Fix (DPI Compatibility)
Seems reasonable... Market is set to a known good number, yet you can change the dpi to whatevery you find appealing.
That thread had a link to a Market app with similar functionality, LCD Density Modder
Here's the discussion on XDA for that app: [APP][2.2+] LCD Density Modder | ICS Compatible | Market Compatibility Fix - xda-developers
Note the Pro version ($2.99) is required to download fixed markets or save your dpi to "favorites". Also, if you install the free version on a different device, you better note what your stock dpi was since it apparently doesn't save that, instead giving you a number of "standard" dpi's (120, 160, 240, 320) to choose from.
If you choose to edit your build.prop file, a backup of your build.prop file is created, making it easy to revert (in theory).
Always make a backup in recovery
before messing with your build.prop file, changing dpi or installing apps like this. Should you goof it up and apps crash or your device is unbootable, restoring a backup OR flashing your rom again are two easy fixes.