We've been hearing a lot of reports from customers that they're having trouble installing the express skus under pretty normal system setups. The setup team is working very hard to fix these issues and to get updated setups to help alleviate these issues.
In the meantime i'm going to try dogfooding the install to see if I run into any issues which I can then tell them about.
I'll let you know more if there are any updates about this issue in the next few days.
Edit: I'm rather impressed. I filled out my registration information and was prompted to run the vcsexpress.exe installer program. I was given the option to install Sql Express and MSDN express. However, since that would have been like 250 MB more, I opted against it leaving the install size at 50 MB. I was then presented with the following screen:
Everything downloaded fine and the installer ran for about 20-30 minutes while I ate. At the end, there was no ask to reboot or anything. I was pretty happy about that given that in installed the entire .net framework. Afterwards I was able to open the editor and make my own project without a hitch.