Having performed merges on branches a few times (during last year's SoC, and also an earlier branch - "branches/animsys2") has not left me with a very favorable impression of this method of version control (in SVN at least. I'm not sure how well some of the distributed systems cope with this in practice, but perhaps it might be a bit better).
In my experience, performing a branch merge using TortoiseSVN + the Blender SVN server is a very dog-slow procedure. It takes upwards of 3 hours a pop, and often with no guarantees of success (either from choosing the wrong revisions, or connection failure halfway when computer goes on standby or otherwise). In contrast, simply updating from trunk or a branch and then saving out patches, gives nice 30 sec to 1 min updates to keep your sources up to date.
Keep in mind too, that these figures were from a year ago. It's now a year later, and the rate of commit activity on Blender's sources has increased (and so have the number of people accessing the server at any given time). Imagine what the merging times are now...
Given these circumstances, would you be wary of merging? ;)