I've had the stuck obtaining IP address issue also. Usually it is at a public wifi spot where resetting the router is not a privilege I enjoy. Most times it is resolved by turning wifi off and waiting, but sometimes rebooting the tab is required. I've had similar issues with older laptops as well. Sleep mode seems to be the worst culprit. The sleeping device doesn't "officially release the IP address so it thinks it can just pick it back up and that's not always the case, especially on a relatively busy network.
And as someone pointed out, setting a static IP address for any "mobile" unit can cause many problems, particularly if your tab or laptop logs onto many different networks during the course of its travels. I usually avoid static IPs for anything but printers of other network devices like APs or routers.
What's is your wifi sleep policy?