I've this personal opinion and I'm trying to validate it: I think that user feel touchscreen device such as iPhone and iPad more personal and intimate because they physically touch the device, unlike the computer where they have one more level of relationship (they use not touch a mouse or a keyboard). Anyone can support this idea? Are some studies that prove this?
Google recently released a study, Understanding Tablet Use: A Multi-Method Exploration, that concluded that 'Tablets Are For Games And Email, Mostly Used On Couch & In Bed' (Techcrunch).
Perhaps it is both a matter of touch and environment that affect our feelings towards a device. Sitting on my comfy couch touching a friend's information profile feels more personal than if I were doing the same activity sitting upright staring at a desktop computer manipulated by a mouse. I would guess that how our physiology is effected while using such a device has an impact on how we feel about said device.
(note: only 33 participants were used for the study)
I agree with Captain—mobile devices are personal by design; without the ability to have multiple users on the device and the sheer amount of time people spend with their phones etc. mean they're naturally more individual than PCs. Large form factor touch devices like kiosks are generally deployed in public scenarios, so if anything they're more shared and thus less personal.
I do a lot of work with kiosks though, so my own experience is different to most. It would be an interesting hypothesis to test but I'm not immediately sure how you'd do so.
I'd say this very well may be a generational issue. I know I find it more personal partially because it's compact and the screen isn't viewed by everyone around me. However those with less finger dexterity might find that it's frustrating rather than intimate. While this is strictly anecdotal, most studies on the issue are going to be dubious at best. If you went on M-Turk and ran your own survey asking users whether they think a touch screen is more or less intimate, I think you'll find the results are inconclusive.
The mobile devices formed a deep relationship within their users well before they had touch capabilities. In the 90's when cell phones started to become the average Joe gadget it quickly also became a very central item in our every day life, and this was before Facebook, phone cameras, phone mp3 players, phone Internet browsing or application utilization as a whole.
It's a tool for getting in touch with the people you like, and for the people you like to get in touch with you. It's an extension of your social communication, something that is very important for everyone.
That is why we form such a commitment to this quirky little device, not because you touch it to interact and somehow suddenly you think it's a puppy or something.