I can only echo the praise of the other reviews here. It's a delightful film with a feelgood factor that it achieves without crossing the line into soppy sentimentality. Naturally sweet - no added sugar.
One small point: it seems to me that the mild objections raised about Ustinov's character Pendelton being able to walk in and defeat the system security ignore the fact that Pendelton is clearly a genius/savant at this sort of thing. Yes, the film was pretty computer illiterate, but it did show Pendelton 'studying computers' at his flat, and I believe the implication was supposed to be that his gifts allowed him to simply engulf the whole subject, practically overnight.
There were a few odd moments when it appeared in some scenes that Gnatpole was trying to test Pendelton's knowledge and call his bluff. I'm not sure whether we were supposed to believe that Pendelton cunningly weaselled his way out of these situations, or whether he was actually knowledgeable enough to pass the tests - it was a little unclear.
Certainly he had to know enough to set up the dummy accounts. Presumably Wallach and Ustinov were relying on their own rather foggy notion of how computers worked in those days, and in order to understand in detail what they were getting at, it's necessary to know quite what their concept was. They knew there was something about 'procedures' which was important; they thought that the 'smart light' could actually control security, rather than just indicate its state; they thought that the (dumb) user terminal's features would strongly influence what could be done on the mainframe itself - though apart from things like graphics feature I don't see it meself.
Mostly, I think they tried to avoid the subject of actual computer operations as far as they could, and they did that rather well. Allowing them a bit of artistic license, I don't think their efforts had any flaws worthy of note.
CD