Well, since I run Eberron almost exclusively, here goes:
I'll probably allow 'em, But I'd like to see 'em first. If they are literally born-of-dragons, no way is a PC being one ('less he's got a BRILLIANT backstory and hooks), as they'd probably be the 4e equivalent of half-dragons, which are EXTREMELY rare. (I'll use the same tack on Tieflings - the one I currently use for all planetouched, as a matter of fact. Very rare and all.) If they aren't literally born-of-dragons, but still draconic, they'll be from argonnessen, so likely not to make it into a campaign any time soon, except as NPCs.
If they're closer to Lizardfolk, I'll probably just use them for that, unless the mechanics reflect a more 'civilized' lizardman - in which case I'll use whatever they have in the MM as lizardfolk.
As for gnomes, I WANT THEM! The Trust is just too cool NOT to have them!