A one-click subscribe button implies that the process is as easy as that, subscribe and it works, but that's not true. It makes it easier to get the files, but you'll still have to worry about compatibility.
EDIT And with compatibility I mean load-order and merging forms (leveled lists and such).
I suppose that in theory (and this is just wild speculation

) it'd be possible for Steam Workshop to include an automated conflict checker. Any .esp uploaded could be scanned against the other uploaded .esp's for conflicting records, then the mods flagged accordingly. Then (as with the Team Fortress items) mods that conflict with the one's you've subscribed to will be hidden by default.
That wouldn't help with
resolving conflicts, but it would at least let newbies avoid them. Of course, if there end up being vast numbers of mods, the scanning may take a while, as it'd be a low-priority for the servers, but I doubt that it'd take more than a couple of hours.
I wonder if they'll use a system like this?