Also, if I install the latest daily build today, will it notify for the update of the stable release when Ubuntu+1 is officially announced?
First, remember that a development build of Ubuntu is exactly that - a development build. So things will break.
With that being said, your mileage may vary.
Second, if you run
sudo apt-get update && sudo apt-get upgrade) fairly frequently (Read: Daily), on release day in theory you will be on the same Ubuntu as everyone else - although I don't recommend using a Ubuntu+1 install for daily usage, even after release day.
It's better to just start fresh, or to upgrade your previous Ubuntu stable installation, if you're into that kind of thing.
Lastly (and I can't stress this enough) if you're not a developer, you really shouldn't be running the development version.
The problems with daily builds during this phase of the release cycle are typically installation failures for one reason or another, rather than problems once you actually start trying to use it on the desktop. If it installs fine for you, you can continuously upgrade to the stable release and beyond.
How useful the development daily images are depends very much on which part of the development cycle we're in. During the alphas, there is a high degree of churn and daily breakage is frequent. They are very useful for developers, but not recommended for general desktop users. As we get to the beta phases of a release, things are generally much more stable and usable for general desktop users to try things out.
Firstly, whether a daily build is stable enough for daily usage mostly depends on your ability to troubleshoot problems. Secondly, the question was asked late April 2011, seven days before release day of Ubuntu 11.04. If you're seven days away from release day, if you have a working OS on your computer, I'd recommend waiting until release day. If you don't have a working OS on your computer, you're closer to release day than to the date the most recent alpha/beta was released, go for it.
What I recommend is to check the release schedule. If the feature freezes haven't kicked in yet, you could end up with very unpredictable results.
Another thing you can do is run the daily build as a virtual machine (virtualbox, vmware, etc.), and set it up as you normally would (extra repositories, run updates, etc.). Once you've tested it as a virtual machine and are confident that you can install it to your computer without trouble, go for it. Be warned, you may end up with irreversible problems where the easiest solution is to do a fresh install.
Lastly, as always, back everything up before you consider reformatting your OS partition.