I fly Copa very frequently. The 25% PQM bonus (as stated by others here) does often take a while to post, but it has always posted for me eventually. This, of course, assumes that I actually booked it on copa.com. I made the mistake of booking a Copa flight on UA's site recently in an attempt to better organize my itineraries. Cost me nearly 1,000 bonus miles. Fortunately, it's not going to make a difference in this year's 1K qualification, as I'm at 102,XXX booked and paid for right now.
I currently live in Costa Rica, and I try to fly Copa whenever possible. The 25% bonus is one reason, but the UG percentages are much higher, and the food in F is usually very, very good with at least two options, usually three. They serve free food in both cabins even on short flights like SJO-PTY. It's a real treat and so different from some of the stuff UA serves.
The downside: The IFE is quite lacking on most of their fleet, and I don't think I have ever seen in seat power, even in F. If anything goes wrong, I never get a response from writing to their customer service department. (I once got a problem resolved by writing directly to the CEO, who answered me personally and promptly.)
Overall, however, they are a great airline, IMO. The inflight service is frequently much better than any U.S. airline. The planes are very clean, with many of them quite new. Depending on your departure city and date, it might be a rare chance for a Silver to get an UG. My last flight from MCO-PTY had only 7 of 16 F seats occupied.