@2) Maybe in an older version, but not anymore. The installation is not as nice as in a single apt-get call, but the install documentation makes a setup a matter of copy'n'paste.
Copying and pasting a few dozen commands and one of them is very likely to fail. I've installed GitLab 3 times and something has failed all 3 times. There's no excuse not to provide a tarball that includes (1) both gitlabhq and gitlab-shell (2) all gems needed. Everything else can be apt-get installed, which is fine. But at least provide a tarball of your application's code.
Been using GitLab since (I think) 4.0 and have yet to experience any problems upgrading on a fairly standard LAMP-like web server setup on a VPS. To anyone having troubles, what exactly are the errors/problems?
(Late) Edit: any problems I've ever had with upgrades have been related to not properly adjusting settings when moving new config files around. For example, in upgrading to 6.3 I failed to copy over my custom listen lines in unicorn for a non-standard port.
I upgrade regularly, typically two weeks after release of a new version (except when there are security fixes, like recently).
It could (and should) be more streamlined, I admit, but using diff et al. on the two affected configuration files makes the process fast. One could do it by hand w/o issues, but I wouldn't like it.