So, if you guys and gals have read the forums or even the minecraft wiki, you might have found out that Minecraft 1.3 comes out tomorrow (August 1st). It probably will come out tomorrow, but note this is a planned release date. Mojang wants to release Minecraft 1.3 on August 1st, but we do not know if they will be able to. Don't be surprised if they fail to release Minecraft 1.3 by then!

Also, when you update to 1.3, make sure you backup your old Minecraft. You will (most likely) not be able to join servers. Most servers don't update instantly to 1.3!
The bukkit team (which makes the software to run servers) also states that they will release a build a little after the 1.3 release.

If you are confused by this, then just do the following:
1.) Do not update your Minecraft
2.) Watch the front page posts on http://bukkit.org/ for a 1.3 update
3.) When they state a version of 1.3 has come out, update your Minecraft!
OR
1.) Backup your Minecraft (put in a safe location)
2.) Update to 1.3
3.) Whenever you want to join a server, install the backup of your Minecraft (only do this if the server is 1.2.5).
4.) Play Server
5.) Whenever you want to play 1.3, repeat steps 1 through 5!

Thank you!
- number1_Master