If you are not an app developer, you really should not be running 4.0. Until the official stable release of 4.0 is out for consumers, there is really no point unless you just want to get your feet wet when it comes to seeing some of the features...
Considering the added functions and content in 4.0 it would not be unreasonable to expect it to take up more memory, as an unfinished beta version it will also contain a bit of transitional junk that will not be in the final release.