Well here in the US actually it seems the PSP and DS are selling roughly equal up to this point? I may be off as it's been a while since I've checked. PSP is more hyped, word of mouth, right now... it's the one everyone WANTS. They are just starting to become common enough that you have like a 50/50 chance that any particular store will have them in stock.
But I know I've heard that in the UK and for a LONG time in Japan the DS was selling much better.
Even if it's not, the point is, sales have not been BAD by any stretch... as I said quite a few of us though the DS would be doomed from the start, overshadowed by the impending PSP... similiar to the way in which many people held off on buying a Dreamcast in favor of waiting for the PS2, which many industry experts agree was a BIG part of the reason the DC failed.