My experience is with a larger age gap than most of our multi-childed friends have; we have 8.5 years between my son (currently 10 and a quarter) and my daughter (currently 1 and three-quarters). Most of our friends have 2 or 3 year age gaps.

Comparing my experience with theirs, the main thing I notice is that we all have our difficult periods at different times and for different reasons. For some specific examples:  
  
 - they often have to deal with two in nappies at once, or an older one potty training while they have a newborn, whereas my son was fully independent (and indeed able to be a real help) by the time my daughter was born  
  
 - I was plunged back into the world of sleepless nights and nappies and sore nipples after a good long gap, during which I had regained my equilibrium as a person, not just as a parent; whereas they get it all over with in one go (it's like the difference between making two small adjustments versus one large one, in some ways)  
  
 - it's sometimes easier for them to find outings or activities that will interest both or all of their children at the same time, whereas we end up doing quite a few things with one child per parent so we can go separate ways as appropriate  
  
 - they often find their children competing for their attention in the same way at the same time, whereas I can multi-task mine quite well (for example doing a puzzle on the floor with my daughter while answering my son's questions about his maths homework) 

These are just a few examples but you get the gist. There are pros and cons each way and while I like my big age gap (the biggest problem has been people assuming that my daughter was a "mistake"!) it may not suit someone else.