Speaking as a member, in terms of actual unionized workplaces affiliated with it, it's still extremely marginal. In terms of membership in general, it has grown considerably in the past few years, but most of the new members are those who were (further) radicalized by the contemporary US politics and seeking like-minded folk in general, not specifically to organize.

Thing is, people who try to organize generally expect some immediate gains out of it, which generally favors large established unions who "play by the rules". IWW is a strongly ideological union and has things like an explicit ban on no-strike clauses in its constitution, which makes it much harder to write a collective bargaining agreement for a workshop that employers are willing to accept. Burgerville Workers Union is a recent example of an IWW success story that broke down over this issue.