My initial impression; running the same YouTube video on my iPhone 3G and DHD - not an intense or incredibly professionally test by any means...
...both speakers sound just as tinny, low quality. The only difference is the 3G goes a bit louder. Possibly some slight distortion at top volume on the DHD.
Not a big problem for me because when I want good quality sound from a speaker (in my car) I use a bluetooth hands free loudspeaker thingy that does a good job.
Apart from that I imagine the DHD will do an addequate job with whatever else I might need it for, which is just YouTube and games really.
If you use speakerphone in phone conversation constantly, or watch a lot of movies without headphones you may find it inadequate.