I use NPM w/browserify without any issues, when im on npm majority of the time module i am looking for states if it will work in browser or not...
For front-end development i symlink some modules into node_modules folder to make it cleaner to require them, instead have relative path hell ie '../../../'
Instead of using bower, or something similar i use napa (npm module), which lets me download something like foundation, right from github and put into my node_modules folder to use in my projects
Personally I like have one system to handle both my server scripting and my front-end as well.
If it works for you then awesome. I just don't like how it feels personally. Also we don't use node on our backend where I work, that may account for my thoughts on the matter.