Heya! I'm a 3+3 right now... I'm entering my third year and am about to take my DAT & app out.
Like chimm said, the 2+3 program is there if you are absolutely sure you want to do dentistry and go to the UoP dent school... you will not get a major and other schools will probably not accept you (besides that crazy girl that got into UCSF, degree in two years.. I know who you're talking about haha). You are not locked into this however and you can drop back to a 3 year and get your degree to expand your options, which is what I am doing (bio degree with chem minor).
You could probably get a degree in 3 years at most colleges if you wanted to do that, but I have to say I have been thoroughly impressed by the professionalism and quality of our bio department. The weeder general bio/general chem classes only help you more to prepare you for the rigorousness of upper division bio courses... They definitely whooped my *** into shape, and after utterly failing the first test, I've been doing spectacular in all of my courses. Grade inflation is a pretty lousy fallback for getting into dent school imo.. if you're having problems passing in undergrad, you'd better get ready for dent school. And also, it's not like pacific is out to fail you; the professors are extremely helpful and want you to pass! There is only one teacher in the department that I would not feel comfortable walking in their office any time of the week.
Also, our ochem here is known for being tough if you take it during the summer (which I did, and didn't do terribly well in... well, first semester was horrible with Franz but second half with Xue was awesome... but I digress). The professors writing my letters of rec do mention that in their recommendations as well, as it is known that summer ochem is hard. Though, like chimm said, you can choose to take it at santa clara or something easier (though when I've been reviewing ochem stuff for the DAT, I still remember things from a year ago)...
For some reason a lot of people like to hate on UoP, but after comparing classes with friends from other universities, it seems that this school is awesome for teaching you the things you need to know to get into whichever dent school you want.
Also, if you are fairly intelligent (which you probably are if you're applying to uop for pre-dentistry) and get accepted into honors, you will probably end up getting a good-sized scholarship.