First and most important, if you are enthusiastic sportsman, you should know this in advance. There will be lot of last minute disappointments for Finnish athletes and teams. Maybe the most famous one is losing to Sweden 2003 in hockey WC in quarter finals after leading 5-1. You can check the pain from here: http://www.youtube.com/watch?v=_ckaCuFfBzA.
There are other good examples. Like Finnish ski jumping national team losing Olympics gold metal with 0,1 points (smallest possible gap) in Salt Lake city. One good one is when Hungary tied in last minute with one of the funniest goals ever made. Win would have taken Finland to WC qualifying. Here's video about that one also: http://www.youtube.com/watch?v=aT-q65Qjy1M.
And there are lot more. Just last week my birth town team lost their continuation in Europa league after leading 3-0 after first period. (http://fin.worldfootball.net/spielbericht/europa-league-qual-2010-2011-3-runde-fc-timisoara-mypa-kouvola/liveticker/#redirect)
So to put it short, if you are sports fanatic and don't have good nerves, just don't come.
Second thing is, if you don't like people complaining about the weather, don't come. That's utmost the most important topic to discuss. There are about 10 days in a year when people think weather is fine.
Couple of those are in April-May when there's around 15-20 and spring has started. Then there might be some good days around Juhannus (mid-summer festival) and then in August when there's again some 25 celsius and it's not too hot or cold. Final ones are Feb-March when there's some snow in the ground, days are getting longer and there's only -5 celcius.
All the other time it's either too cold, windy, rainy, snowy, dark, hot, sunny or something else. You will see how good we are finding reasons to complain about the weather. It's kinda of a hobby to all Finns.
These two are the most important ones I would say.