Canonical announced that Ubuntu 13.04 actually will provide 4 kind of basic ISO installer for various computer, including PC (Intel x86) desktop image, 64-bit PC (AMD64) desktop image, 64-bit Mac (AMD64) desktop image, Mac (PowerPC) and IBM-PPC (POWER5) desktop image. Actually all these release candidates are now available for Download on Ubuntu Images. You can know as well the current development of 13.04 from this homepage.
The Ubuntu 13.04 ISO image installer which can be downloaded on Ubuntu Images homepage is a release candidate. Some bugs are not fixed yet on this version. Canonical states that one of the simple images on these ISO's is related to the size of overall installer files. This image is oversized (which is a bug) and will not fit onto a standard 703MiB CD. To install it, you may need the USB storage or DVD.
As the 13.04 which can be installed now on the computer is a release candidate, it is not recommended for you to install and use it for the stable and important works. Some bugs will appears on this release candidate. You are recommended to install it as the tester only: to now what are news from this ubuntu version.
Ubuntu 13.04 will try to provides a new Ubuntu which fits on mobile. It gives the users the advantages especially for those related to memory of the computer. It will reduce some memory use for some default and installed package. The GTK3 --as part of this version-- will only load CSS images on data when needed. This process will help to reduce the use of memory along the process.