Hey Robbie,
Of course you're never entirely sure what Google will do, but if you're only changing host - nothing else - you should have no problem.
Do not:
- Change ownership of the domain;
- Make any major content changes (such as titles);
- Add large chunks of content - keep it to a minimum;
- Make any website template changes;
It's very important that all that's changing is the host. And of course keep an eye on your rankings while doing the migration. Perhaps use a SEOmoz campaign for that. They also do crawl tests so that should be good.
Good luck!
