A not-bad September for ad-friendly internet radio service Pandora. It treaded water in listener hours in September, but gained slightly in market share and active listeners over August, enjoyed a cheery forecast for mobile advertising, but weathered a threat from Apple. Listener hours for Pandora during the month of September 2012 were 1.15 billion, an increase of 67% from 687 million during the same period last year, but pretty even with August’s 1.16 billion.

Share of total U.S. radio listening for Pandora in September 2012 was 6.53%, an increase from 4.03% at the same time last year, and up from 6.30% in August.

Active listeners were 58.3 million at the end of September 2012, an increase of 49% from 39.0 million during the same time period last year, and up 2.1% over August.

Also in September, eMarketer described Pandora Media as having emerged as "one of the strongest US mobile display ad sellers" with its share of US mobile display revenue expected to reach 20.5% in 2012, compared to 18.4% for Google. Sure, mobile display is a fraction of a fraction; eMarketer believes just 1% of US ad spend for 2012 will be mobile. But Pandora should net over $20 billion and claim bragging rights over Google.

All good news, but Pandora took a punch in September with shares dropping 18% overnight based on a Wall Street Journal report that Apple is creating a service just like it. Ironic, observed Mashable, as "We know Apple is vehemently against being copied [viz., Samsung] but the iPhone maker might be taking a page out of Pandora‘s playbook."