Ok, as i see there are 2 different points of view in here:
1. you had to use slow down dsj, if you wanted to jump at the top of the lists and it is fun, too
2. slow down is cheating, evil, unsportsmanlike
So i will give you a small history of slowdown on DSJ:
I started playing DSJ about 5 years ago on version DSJ2.1. Great physics, great game

A windeditor for setting the wind at a fix value (yes, +20m/s were possible) was existing, so you were able to do amazing jumps and upload your recordlist, but you couldn't proof your jump by replay, because without the windeditor the wind in the replay was normal and so the jump failed

A small DOS-slowdown proggie was also existing (slowdown.com). For using that you had to write a small .bat-file, which started the slowdown-proggie and DSJ in a Batch. Now you were able to slowdown DSJ by several times (ingame). Because of a smaller framerate by slowing down the game too much i used to play DSJ at half speed. The top-players jumped at 1/10, 1/20 or 1/30 speed, but that wasn't fun to me ...
At the end there came out a new windeditor, which worked the following way: Starting DSJ, starting the editor, loading an existing DSJ-Replay with perfect wind into the editor, switching back to DSJ and with a special key you were able to "transfer" the perfect wind from the older replay into the running game. This wind worked in the replay of the actual jump, too ... side-effect: wind-transferring AND slowdown didn't work at the same time

Paradoxically this new "wind editor" was a cheat to the DSJ-community and DSJ2 was DEAD
So we all were waiting for the next version of DSJ, which was published by Jussi in october 2004. The graphics did a huge jump and the feeling in the air was unbelievable. GREAT fun! Some weeks after DSJ3 came out, some guys discovered a slowdown tool named "XSpeed" and this tool worked on DSJ3 perfect (stupidly). Now it was possible (again) to do better jumps (about 10% longer). My first thought: damn! I didn't use it at first, but after a while i tried it by myself. The beginning wasn't easy but after some practice with this tool the fun was a big as at normal speed (maybe even a little bit better *g*). But the wish for a competition at normal (fast) speed was strong all the times up to now. And now we have the online mode

The most important things aren't "analyzing the hill", "waiting for the perfect wind" and "skills on sensiblity" anymore, now the most important things are CONCENTRATION, REACTION and SENSIBILITY
So, my conclusion:
With SlowDown DSJ was a great (competition)game, too. It wasn't fine that you had to use it, if you really wanted to compete, but it wasn't THAT evil and it didn't destroy DSJ, quite the contrary: through tools like XSpeed it was possible to do the perfect jump and this goal let my play DSJ again and again and again ...
Now the last missing thing is a ONLINE-Record-List and everything would be fine ;o) A Offline-Recordlist for "DSJ1.5-only"-jumps would be great, too ...
And now something for cooling down:
http://www.youtube.com/watch?v=ENvg8nK8DaM
(the Sev-Bug)