It's one of those indescribable things that need to be experienced RJH.
On paper I should hate it - I have real difficulties in coping with large numbers of people around (really conversationally I'm hard put to cope with more than 2 people at a time and is one of the reasons why I'm never going to be able to do a 'people-facing' job ever again) and I tend to get panic attacks just going around a supermarket so Birmingham last year had a couple of moments where I had to led off to a gin and tonic away from masses of people laughing and talking.
The cost of attending a con is off-putting I know (especially if you're a group) but even if you just want to do some shopping it's probably worth a day ticket as they have all kinds of things you'd never see in the one place and if you have one taking place near to you and the programme's up well in advance you can cherry pick your days maybe to get into some of the more attractive events. For things like the klatchs you probably do need to be there for the duration to have a chance of getting on one of your 1st or 2nd choice as competition is really full on, especially for Terry's of course and if you want things signed (well, stamped now) then really I think the conventions will be the only game in town from now on.
For me it's a package of things that's the attraction but meeting up with forum friends is right at the top of the list