On my Xh last winter I filmed almost 100% 60i, this summer I filmed a bunch of random scenic stuff on 30p then forgot to switch it back for filming mtn biking, ended up not being that big of a deal at all, overall the edit and the footage came out way better then if it was in 60i and im actually glad I made the mistake. This year i think the only time ill put it to 60i is if im filming a park shoot with a huge table or blower powder.
And just because its 60i doesnt mean its gunna look good at 50% with no other work. I have a few minutes at the end of a tape that needs to get imported... I'll try doing a FCP tutorial next week of a trick my buddy showed me to get super smooth slowmo without twixtor if i have time and there is enough intrest.