Hmmm.. the email I got yesterday for a 1K challenge says the following:
Your status will be effective for 90 days. Your 90 day time frame will be January 1, 2013 through April 1, 2013. To remain a Premier 1K member through 2013, you will need to fly 35,000 Premier qualifying miles (PQM) or 40 Premier qualifying segments (PQS) on flights operated by United®, United Express® or Copa within that 90-day timeframe*.
If you meet the above required PQM or PQS threshold(s), a Premier 1K kit will be issued and mailed to you. Until you have a card, be sure to add your MileagePlus number to your reservation in order to benefit from your Premier status.
*Please note that qualifying activity for this promotion includes only base PQM/PQS and class-of-service bonus PQM/PQS earned on flights operated by United, United Express or Copa, and credited to your MileagePlus account. Any other bonus PQM/PQS, promotional PQM/PQS, credit card PQM, or PQM/PQS earned on other Star Alliance carriers do not count toward qualification for this promotion.
Seems they've clarified the language, but in favor of using the bonus miles.