I bought the HTC Desire as well and that was when I discovered e-reading for me for the first time. It is pretty comfortable to read with its AMOLED-Display and good reading software (like FBReader), especially because you can switch to white text on dark background in the night, and don't need a lightsource.
But if you want to read in the sunshine, it just doesn't work, that's a fact.
So I found that I would like to have an ereader-device as well and just bought a Sony PRS-650 a few weeks ago.
I don't regret buying both devices, the Sony is perfect for reading at home, or in the sun, the Desire I always carry with me (but since I got the Sony I don't really use it for reading any more...).