Well, if you put 60fps in a 30fps timeline you are only going to see every other frame. So that will look slightly odd. Especially on fast motion. You can put 30fps in a 60fps timeline just fine. It will look like 30fps. But it won't look like the smooth motion of the 60fps visuals in the 60fps timeline.
The more frames per second, the better. Television is broadcast at either 720p or 1080i. Both are sixty images per second.
So, if you want to work in a 720p60 sequence, that would cover your bases. The 60p would show as 60p and the 30p would show as 30p. Unfortunately FCP 7 doesn't let you put 60p in a 1080i correctly. It wouldn't map the frames to fields. It would just strip out every other frame. FCP X does perform the operation correctly.
"The more frames per second, the better. Television is broadcast at either 720p or 1080i. Both are sixty images per second"
Really? In the UK I'm pretty sure it's 25p or 50i which equates to 25 images per second, and in the US it's 30P or 60i, which are not 60 images per second...I didn't think broadcast was 60p normally.... but I could be wrong.
EDIT- I suspect I AM wrong because Bret you are far more experienced than I am, so hopefully that didn't come across as arrogant or anything, it was a genuine question :)
Editor, Certified Apple Product Proffessional, 2010
Equipment (not for 'bragging', but in case it's relevant to future posts :D): Canon 7D, with Rode NTG2.
iMac 27" intel i7 3.4GHz, 12GB RAM, ATI HD 6970M [2GB GDDR5], 2x G-Tech G-RAID (0) 2TB over Thunderbolt via Sonnet Echo ExpressCard/34 Thunderbolt adapter and Tempo™ SATA ExpressCard/34. Elgato Turbo H264HD.
Sorry to forget PAL land. But She was referring to NTSC frame rates in her question.
The US is 60hz. Either 720p60 or 1080i30) I would assume pal is 720p50 or 1080i25.
If it wasn't 720p60, then interlaced material shot or played back would look like it does on a computer monitor. I don't completely understand it, but each field gets mapped to a frame of progressive. The reverse is true if you convert 720p60 to 1080i. Each frame gets converted to a field. Pretty seamless. 24p material simply has pulldown added. There no pulldown that matches up with 30p except repeating every 4th frame which on anything but a lock-off looks like hell.