Andy_Langton - 10:00 am on Apr 24, 2012 (gmt 0)
I've moved a number of sites to cloud hosting and similar services over the past year or so, and I've not experienced any problems at all.
It looks like you've spotted the biggest potential issue, which is with geographic targeting, since cloud hosting may not be in your target country when Google visits. But, if you have a regional name like co.uk, I think you're unlikely to see any impact at all.
If your new host is unreliable or there is downtime, then you might see a few blips, but my personal experience has been that it won't cause any problems.