As per the various sources over the internet. Ubuntu 12.04 LTS release date is 26 April 2012. However, Ubuntu 12.04 is available on the repositories online. I have been using both of them. That’s the two LTS versions, Ubuntu 10.04 LTS and Ubuntu 12.04 LTS (pre-released). Those of you trying Ubuntu for the first time should go with Ubuntu 10.04 LTS, as that version is supported and much more stable. Ubuntu 10.04 Lucid Lynx will be supported till the October of 2012. So that shouldn’t be an issue for any one. Moreover the upgrade can later on be made from Ubuntu 10.04 LTS Lucid Lynx to Ubuntu 12.04 LTS Precise Pangolin. Various issues faced on Ubuntu 12.04 pre release were mainly stability of the GUI and applications terminating unexpectedly. Also this fact must be considered that a downgraded version of GNOME was being used. I had installed a previous version of the GNOME, the GNOME classic, and not the bundled version GNOME Unity (which I didn’t happen to use much so far).
The driver support in Ubuntu 12.04 is much better than the Ubuntu 10.04 (eg. WiFi adapter). So you may consider this fact in your decision-making process as well. If you proceed with the Ubuntu 10.04 installation, and have troubles connecting to the internet and configuring Wi-Fi. Rather go with Ubuntu 12.04, as mentioned, it has a much-much better support for your hardware, and will probably run ok.