I have a 3 year old dalmation and she runs with me every morning and loves (well she looks like she's smiling to me).
She's naturally built up to 14km with me and as I'm training for a marathon she'll eventually get up to that distance too. I run with a lead as she is completely deaf and can't let her off; she'll also very "playful" with other dogs and purches which is why I won't use a harness.
It's for a great cause - no doubt. But they don't market it as a fun run do they? It does make a mockery of having a system of queuing the runners by expected time though.
@Grendel3 - it's the Hull Run4All 10k on 3rd June. I think the urge to go off too quick will be an issue but I can only trust myself to keep something back.