With JavaScript and the GPL it is very unclear what "linking" is. Probably your entire website becomes GPL including content. Who knows as the language was written for system libraries. So I can see lawyers having an issue.
If you are not intending to modify Mongo then AGPL is not restrictive, which may be OK. The database API is not usually considered as "linking" as it is a wire protocol.
It remind me a few months ago the launch of meteor.js. I heard so much people saying that it was "not usable commercially"...
And the worse is that the same people have MongoDB in production with it's AGPL license.