A few ISP/IP comments from a soon to be ISP grad:
1. You have LOTS of time to make that decision. I agree that the choice between the two pathways is very attractive and something that sets OSU apart, but no need to stress about it now. You will get the opportunity to talk to your anatomy proctors (who will mostly be ISP Med 2s), numerous panel discussions will be held (will students from all levels), and the opportunity to talk with students for a good two months about their choices.
2. Re: never seeing the ISP people again - I think this varies highly on the individual. If people disappear from the radar, its largely by their own choice and they would likely disappear even if they were doing IP. Everyone has anatomy together for something like 14 weeks - lots of friendships are established long before people choose pathways. Everyone continues to take the CAPS course together - so you will still see ISP people there. Many ISPers are very active in various student activities. I made a point to try and socialize when I came to campus and be involved with activities because I did want to be involved and see my classmates.
3. Lonliness - again, what you make of it. We had a LOT of students my year do ISP (like 60 people). Many of the ISP students take advantage of the ISP library to do all of their studying and it's almost like an office/job environment. People come in at 7-8 am, and study until 3-5. People often take snack/lunch breaks together. Other people choose to never come to campus unless they have to.
4. Re: books - while there are a lot of books in the ISP library, I still ended up buying the vast majority of my texts. If you happen to be one of the few people who are ahead of schedule (or really far behind), you can get away without buying many texts, because you will be the first one to need a book. However, there are definitely not enough books to go around.
5. ISP for "special circumstances": While I do think a lot of people choose ISP because of family obligations, I think the majority of people choose it for the flexibility. Although there are a lot of people who do IP but never go to lecture, they are still obligated to take their exams when scheduled with very little flexibility. You better hope that your sister/brother doesn't schedule their wedding on the west coast the Saturday after the exam because policy is that you will NOT be allowed to take your exam at early/at a different time so you can make the rehearsal dinner on Friday night. Same thing with holidays - if there is an exam before a holiday break, you are forced to wait until after the exam to fly out. It was very nice on ISP to set my own test date (within limits) based on what worked best for me. If I was sick for a couple of days, I could move my test date back a couple of days instead of having to take an exam I wasn't ready for.
Also with the flexibility - I think ISP gives you a bit more freedom in doing research, but plenty of IP students do research between M1 and M2.
6. ISPers hard to find: I'm not sure how many people are doing ISP, but the vast majority of students do IP. We always had a good mix of IPers vs ISPers at interview days, but it tends to be related to test deadlines for both pathways in terms of who comes to lunch/tours. I do think the number went down dramatically after they started podcasting the lectures. My year (I'm a 5th year dual degree student) was the last class to not have podcasting, but we still had 3 times as many people choose ISP as the year before.
7. There seemed to be a perception out there that all of the "gunners" did ISP. I know some people who chose IP because they thought it would be easier to excel there vs. more competitive to be at the top of the class in IP. (And yes, I know we're non-ranking and blah, blah, blah - but they do still give an award at the end of the year for the top student in IP/ISP/CAPS as well as honors and letters to the top 25%, so this can be an issue for those gunning for AOA, etc.) In any case, I don't know that this is really the case. There were definitely a fair amount of less motivated students in my class who did ISP and a lot of us who were just happy with being average.
8. Additional time to study for Step 1: eh - don't base your decision on this. Just as many people (if not more) end up running behind in ISP and having less time to study as end up finishing early and having more (or just more vacation time).
Ultimately, you will be well educated no matter which path you choose. You will hear stories of people doing better/worse in clinicals depending on pathways, but I think those are largely myths. And again - it's WAY too early to start obsessing about pathways. Enjoy the rest of your time before med school starts.