Depends on the freeroll. I play most nights on the empire 500 dollar freeroll as it suits the time when i have just bathed the kids and settled down(obviously this is also the time the wife starts to watch her hour and a half of soaps on UK telly that happens every weekday night)...i usually get into the top 500 on this site and then it turns into a bit of a lucky dip due to people stalling with small chip counts and hoping that the software will hop them from table to table keeping em from that rapidly ever bigger blind. My experience with these and other freerolls are that from this point until final table it is mostly pure luck. so if you play on the large player count freerolls i would surmise luck playing a large part, However on the smaller little know or limited player freerolls(say about 500 max)...a determined semi skilled player can usually do quite well if they are serious in thier play and not there because they stumbled across the game or waiting between other more important tourneys.
The most money i ever won in a freeroll was 15 dollars for coming 7th out of 2000 players and 18 dollars from my first ever cards chat freeroll (I thought at the time 'wow I'm so good at this' but later on seen that this was just luck and juiceeq wasn't playin)....so in essence, unless you finish in the top three to five...the money is not so good..but you always feel good when you make that final table...Hence i personally feel more sucessfull after a good freeroll placing.
Buy in tourneys offer better odds
on your playing time/ profit margin, but only if you you do well. The bottom line for me is that playing big free tourneys for fun is enjoyable and i play better when i get nearer the last few hundred...and money tourneys i have paid for are more serious and sometimes painfully slow and sometimes no fun at all( not all the time as i have lost out many the time in a sit n go tourney but enjoyed the game play).
Thats my take on things however if anyone wants to correct me on my assumption of the lucky dip part of a large freeroll ...do point me in the right direction on how i get bye that stage