When i applied to go back to uni (i didn't finish my first degree because it wasn't for me, my parents pushed me into a subject that i wasn't interested in and pretty much blackmailed me with a flat to live in so that i'd do what they wanted) i applied to six courses at three unis, i applied quite late in the day possibly just before or just after the UCAS deadline. One uni offered me an interview but i couldn't make the day they gave me so they interviewed me over the phone and then gave me an unconditional offer.
Swansea, the uni i wanted to go to offered me an interview which i went to and was then offered an unconditional place, the third uni didn't get back to me before i accepted Swansea as my first choice, the other uni that gave me an offer was my reserve but with an unconditional from Swansea i was never going to need that. After i accepted Swansea the third uni offered me a place (i think the offer must have crossed with me accepting the Swansea offer in the post).
My point is that i was offered a place with one uni after a telephone interview because i told them i couldn't make the date they gave me, (can't remember the reason, it could have been because it was short notice and i couldn't get the time off work or it might have been because it was around the same time as i spent some time in hospital for an operation). Another uni offered me a place without even getting in touch with me and my uni of choice offered me a place after interview, (but while i was at interview i was told by a postgrad who was showing people around the department that they invite the people they want to make offers to, to interview just to make sure they are genuinely interested in the subject, but unless they screw up royally at interview they have their place).
Obviously my experience there wasn't Durham. At Durham i applied as a post grad and came for an interview for my place, when i was offered my place i was told in the email that my, 'performance at interview convinced us (the lecturers who interviewed me) that you should be offerd a place at Durham'. Clearly the interview was an important factor in me receiving my offer but if they didn't interview, whether i came to an open day or not wouldn't have made a difference. As it happens my interview wasn't on the same day as an open day so technically i haven't attended an open day.
I actually applied for my college without having looked around it, i grew up near Durham so knew a little bit about the college and knew that i would apply for either Hatfield or Castle, in the end i made my decision from what i read on the website, i then visited my college and had a look around after i accepted my offer and just happened to be in Durham one day and emailed ahead to see if someone could show me around.