Like Hilary, October is our favourite time to visit Orlando. We've always been lucky with the weather and crowds. We were there for 3 weeks from 12 October (2002) and apart from Mickey's Not So Scary Halloween Party which was <i>mobbed</i> (more about that later), we found everything very quiet - almost too quiet at Epcot on a couple of occasions. I'm convinced the trick is in avoiding Early Entry days (or whatever they're called these days) and would do so even if we stayed onsite.
Quite apart from the weather and low crowds, I would visit in October for the Food and Wine Festival alone. We just love spending the whole day grazing our way around World Showcase. In fact we always visit twice because we find we're full by about half way around the lagoon! We work clockwise one time and then anti-clockwise the next.
We did
MNSSHP for the first time in October and for the first time ever I felt duped by the Disney Corporation. In my opinion it's just an excuse to extract extra cash from you for the privilege of entering the park during the evening. If you visited during the longer summer opening hours, evening entry would be included in your regular park admission. OK, there is a bespoke parade, but it's not that great, especially when you compare it with the other evening MK parade, SpectroMagic. We did that for the first time last trip too and it really is awesome. There are the 'Trick or Treat' lines for sweets, which I'm sure is quite fun for the little ones, but the queues are horrendous, although they move fairly quickly. As for getting near any rides - forget it! We did
MVMCP in December, 2001 and, although it is a very similar event, I didn't come away with the same feeling of having been ripped off. The atmosphere was much different and I guess I got taken in with the snow on Main Street! Having said all that; many many people love it, so go along and decide for yourselves.
Halloween Horror Nights - now that's another story altogether! We did it back in 1998 at Universal Studios and again last October at IoA. It's a very grown-up event with the potential to be quite scary, although it hasn't bothered me either time. I am easily scared, but the trick is to be (or rather appear to be!) very nonchalant when approached by the scare actors. Scream and run away and they come after you all the more - elder dd (aged 17) learned that one the hard way! The prices for the event are a bit of a minefield - peak nights (normally Fridays and Saturdays) are expensive. We had intended to go on Saturday 19th as it was our friends' son's 21st birthday and we were staying at HRH. Being Annual Passholders, we were entitled to a reduced rate and because we were hotel guests, we were guaranteed admission even though it was sold out. However, we were advised by both park staff and hotel staff to avoid it at all costs. We ended up going the following Wednesday, which was very manageable in terms of crowds. Saturdays tend to sell out so, unless you are a Universal Resort guest, you will need to book in advance (and possibly for other peak nights). Week nights you will have no problem.
Costumes are allowed at MNSSHP (and many people do dress up). At
HHN, costumes are not permitted.
We visited both in October this - oops - last year! 
every ride was walk on
