[NotUncivil]

>millions of pageviews/month

That is technically correct but does not covey the scale at which 4chan operates. According to http://www.4chan.org/advertise,

    Page impressions per month: 575,000,000;
    Unique visitors per month: 25,000,000;
    Posts per day: 1,000,000; 
    Alexa Traffic Rank: 836 (Global) & 371 (US)
    Quantcast Rank: 305 (US)
    Google PageRank: 6

Makes me wonder if WebM will increase or reduce 4chan's total traffic (when measured in bytes, not clicks).

[Igglyboo]

I can't imagine WebM impacting 4chan anytime soon, it will probably reduce 4chan's load when(if) WebM takes off but I highly doubt more than a small fraction will choose WebM over a .gif in the immediate future.

[Robadob]

WebM has caused longer animated content to be posted that wouldn't have been so possible as gifs (the limit is at 2 minutes iirc), so there will still be people posting large files.