If the only reason for considering the pass is for line skipping, I wouldn't buy it.
There are only three attractions in Rome where queues are long enough to worry about: the Vatican museums and St Peters- which the Roma Pass does not cover - and the Colosseum.
The only way to get around queues at the Vatican Museums is to pre-purchase tickets or a tour. The security-check line at the basilica is what it is unless you've booked a tour of the museums which also includes the church.Tickets for the Colosseum/Forum/Palatine are only € 12.00 if purchased at any of the three attractions, and you can often get around that queue at the Colosseum simply by purchasing your tickets at the Palatine where lines are shortest. As everyone has to pass through a security check at all three, you may have to deal with a short wait depending on how mobbed it is.
We've never seen a queue worth worrying much about - or that we could do anything about, such as a long one at the Palatine one day - anywhere else in Rome but that's just been our experience.
Don't be confused by the "free entrance" claim: you definitely pay for those entrances when you buy the pass, and the concessionary reductions for additional attractions are pretty small. It's not easy to cram enough in to make it pay if you are not going to use it for transport - which is really the biggest piece of any cost saving if you use buses and/or metro enough - and will be forking over additional ABOVE the pass prices for concessionary entrances. Again, you have to do the math carefully, and consider all the FREE attractions, such as almost all of the churches, as well.
Traveling Woman, there is technically no three-day Roma Pass: it expires in 48 hours so if you first use it say, at 8:00 AM on Saturday, it expires at 8:00 AM on Monday You could make it stretch 2 partial and one full day by activating, say, midday on Saturday, in which case if would expire at midday on Monday. BUT, Monday is also the day the National Museums are closed, and you have a morning tour that day anyway. And honestly, attractions and museums are scattered all over central Rome so without taking transport, I don't know how much you can fit in without very careful grouping of sites by area. Hope that makes sense?
For the Borghese, here's the procedure for making reservations if intending on using the Roma Pass for that one:
http://www.romapass.it/p.aspx?l=en&tid=33#faqq38