Last Thursday 7/25 saw a spike in new account registrations (5,814) for enwiki [1], making it the 4th highest converting day for daily registrations in the last 2 years. The spike was not due to campaigns such as login CTA or anon edit warning [2] or mobile registrations [3]. We're not running new acquisition campaigns and I suspect the cause might be the fundraiser (I'll check with them on the timing of campaigns targeting enwiki). There might be also external causes we're not aware of.
Aside from this single peak, the hourly trend suggests that the gradual year-to-year decline in new registrations has considerably slowed down [4], which is certainly great news for editor engagement on the English Wikipedia.
Dario
[1] http://ee-dashboard.wmflabs.org/graphs/enwiki_daily_reg [2] http://ee-dashboard.wmflabs.org/graphs/enwiki_campaigns [3] http://ee-dashboard.wmflabs.org/graphs/enwiki_daily_reg_mobile [4] http://ee-dashboard.wmflabs.org/graphs/enwiki_hourly_reg_y2y