The build quality on the Eris looks good.
However, if you are going to be in a marginal signal area, the Moto Droid is much better at pulling in weak signals. My wife's Eris drops calls (-97 dBm to 0 signal) while my Droid does not drop calls (-86 to -89 dBm) when side by side. We thought the Eris was defective, so we exchanged it for a new one, but the new one is the same. My niece's Hero is also exhibiting the same low signal as the 2 Eris phones.
Sorry for the off-topic post, but I thought you would like to know, as that is the main purpose of a phone, to function as a phone first and foremost.
Edit: Did the PRL update today to 51716 and the signal is acceptable now. Still on the weak side (-89 dBm), but it shouldn't be dropping calls now.