Wanderlass, you have entirely different experience to myself and a couple of my friends then - as in more than one overseas airport and in Manila airports when checking in for an International Cebu Pacific flight, I have had Cebu Pacific staff tell me that (prepaid) sports equipment baggage cannot weigh more than 15kg, and no I cannot pack that 15kg sports gear in with 15kg normal baggage allowance into one bag/case.
I was even told by ground staff that as my sports gear weighed 19kg they wanted to charge me 4kg excess baggage for it, regardless of fact my 'allowed' 15kg normal baggage only weighed about 8kg.
Ditto - I had this exact same problem on two occasions with Cebu pacific - At Cebu airport both times I think!
I now tend to aim for Philippine Airlines flights where possible, you can pick up a Sports Plus card for $30US a year which gives you the additional 15kg baggage on every domestic flight at no additional cost.
The PAL fares tend to be higher closer to the time of travel but are actually often cheaper if booked in advance - I booked return flights to Cebu from Manila for the end of November last week and paid a total of less than 3,100 PHP for two return flights - i.e. less than 800 PHP per flight!
The big disadvantage of PAL is they are a lot more strict on the carry-on limits. I've never had a carry-on bag rejected from Cebu Pacific, including my DSLR and housing set-up which is a real struggle to get into the overhead compartment. However, when travelling with PAL there is normally someone to measure and weigh all bags straight after check-in - I'm going to try the 'disposable' bags next time though
I normally carry on my DSLR and lens as hand luggage and check in everything else, for a full set of tech kit and the DSLR housing, ports and and strobes, plus luggage for two people I normally need to pay about 2 or 3 kilos excess on my standard allowance of (20+20+15) 55kgs - at the end of the day 200-300 Php isn't too much! On the way back the weight seems to grow by another 3 or 4 kilos - I really need to dry kit better before coming back!
In short Cebu Pacific are pretty relaxed about carry-on but normally sharp on any potential excess baggage fees for check-in - The per bag and per person rules seem to get used a lot with Cebu Pacific to give you excess baggage charges even if you're within your total 'allowed' weight. PAL are a lot more strict on the carry-on but in my opinion tend to have a better policy on check-in luggage - although they'll still charge you for any excess weight!
Karl