I've seen a few examples - some myself and some from others - of issues getting My Sites created in beta 2 of SharePoint 2013. It can be a little tough to track down, because we use a queued approach now to creating personal sites, so you need to do a little digging to track down what's going on. If you do some snooping around the ULS logs, you'll see that creation of personal sites are managed by a timer job, which ends up being the "My Site Instantiation Interactive Request Queue" job. There is one per web application, so there's basically a three part process you want to go through:
I followed this methodology to track down an issue that's been plaguing me for a few weeks, and was subsequently able to resolve it.
Good point Steve! Stuck timer service jobs are one of those should-always-check rules, and since SP2013 makes ever more use of timer service jobs (e.g. 'Demo SIte Upgrade') its more critical.