Hi :)
On my own machine at home and at work I think it is a good policy to download and install new versions of new branches asap. Preferably even at beta-release stage (ie pre-release). That allows me to test out all the features i think i use and play around to see if it feels alright.
Then i can post bug-reports while the devs are still most keen and most focussed on fixing things and smoothing it out. It's not always quick to fix but it helps the devs. It might be really great if people could test out a new branch at pre-release stage and then go through some of the existing bug-reports to quickly see if they are still a problem with the newer release. That might really help the devs.
Of course on colleagues machines i stick with the stable branch. Any release after x.x.3 is much more stable, with x.x.6 being about as rock-solid as it's possible to get.
The question is are you happy to just sit&hope that someone else happens to notice issues that you personally find crucial? I'd rather have an active say in pushing forwards things that i want to see fixed.
After having a test drive i can always reinstall the older version if i need to/ "Simples" 
Errr, in the case of the 4.0.0 i got really lucky and found everything i cared about just seems to work! WooHooo 
Regards from
Tom 