I've got a new iphone (only had it for 5 days) which I am still having a lot of fun in the playing with everything stage (helped by a $50 itunes voucher I got for Christmas and hadn't used, so I'm pretty relaxed about a bit of playing with moderately priced paid apps as well as the free ones).

I downloaded MotionX-GPS (NZ$4.19 - will be cheaper in $U.S. and there is a 'lite' version which is free) and used it on my ride today. First thing is - yes it is a battery hog. Battery went from 90% to 55% on a two hour ride (yes I have a battery monitoring app as well).

Pretty easy to use though, found the satellite much quicker than my old Garmin 205. I had it in my jersey pocket so I didn't use it for monitoring as I was going (I've got a computer on my bike). I emailed the track to myself (from the iphone) and manually added it to my Garmin connect account. The track was accurate when superimposed on google maps and all features including player worked.

I might give the free version of iMaymyRide a go tomorrow (again there is a free lite version and a fuller version)

I'd definitely recommend that any cyclist with an iphone have a go with the (possibly the free versions of) some GPS apps. However, my assessment would be that the battery issue makes it not great for using as your main cycle computer. I'd also want my phone so wrapped up in the rain that it might affect the GPS signal). But if you just occassionally want to have a play with GPS the apps look pretty good.