I can't realy say + signs are dangerous,
but I consider them 'bad style'.
I'm a Java / Oracle / Web / Bash whatever developer
coding in a mixed Linux and win32 enviroment
AFAIK a + must be urlencoded when used in links,
our documents are often linked,
so not using these kind of characters in the first place
saves a lot of headaches later.
(I dont use spaces in my filenames either,
for pretty much the same reasons)
I wouldn't say it is dangerous,
but mark my words:
one day you will understand what I have told you