I know every PBS is different, but it really isn't horrible (depending on the system you use). When we started PBS at DL I had 11 years seniority-granted I was based in NYC, which made me artificially senior compared to most bases.
Some of the things I liked about it:
1) No more carry-over trips from month-to-month. This meant not having to pick something up in the first 5 days of the month if you caused a conflict (or risk being assigned).
2) The end of reserve. We switched to the infamous "A" day system. At that time everyone (except the top 25% in each base) had either 3 or 6 days of reserve each month depending on seniority. I had 3 days monthly for about 6 months, which then dropped to 0 (and I wasn't even in the top 25%). You could preference trips for your A Days and if they were available, you got them. Of my 6 months on A Days, I just preferenced "any International", and got 4 international trips, one domestic, and once where I sat on call for 3 days after doing airport standby. The things I liked about getting assigned trips was I hated being at their mercy! I could never sleep waiting for the phone to ring.
3) Jetway trades/partial trip trades. More flexibility.
4) "Real time" trades with each other AND Open time. First-come, first-served. I loved this. I know MANY senior people who thinks it's a travesty that junior people might get a trip they want. I thought it was more than fair. You already get weekends and holidays OFF (and have since the 80's) why shouldn't pick-ups/trades with open time at least be fair to everyone trying? Just my 0.02
Things I didn't like:
1) Extremely confusing at first. Takes many months of mistakes before you get it right. Even then, when you did make a mistake, a scheduling manager would tell you what you did wrong-all to no avail. I still couldn't get it. He/she could have lied to me for all I know.
2) Vacation sucks. No more dropping all trips that touch a vacation day. With PBS maxamizing time-off around vacation is tricky. In fact, I know some who only got 7 days OFF from their 7 day vacation stretch (where with the older system you could really get 14 or >).
3) More > 3 hour sits at hubs (at least it felt like it)
4) Sick time reduced to 42.5 hours per year TOTAL.
Now, I can't say if all this was caused by PBS or if some came right before/after (so some may have nothing to do with PBS). All of this information is anecdotal, so take it with a grain of salt. Also, I left in 2008, right before the merger, so I'm not sure if things are exactly the same or not.