I too have been using Trailguru for a few days. Clever. I also turn off WIFI, Auto Lock and Bluetooth. iPhone will try to grab every wifi station on the road as you pass into range so it probably taxes the iPhone a bit there.

I play tunes in the background while Trailguru is running foreground and it works. I have a Belkin sports band to carry the iPhone on my arm. Works ok (not so good for skinny arms). I just put the phone into the carrier upside down so the speaker is pointing up and out of the pocket. I can easily hear cars and other road noise with the tunes playing. Did I mention I don't use ear buds. Have enough trouble with my ears as it is.

There are a couple other iPhone apps out there that I have installed on the iPhone. GoLearn Cycling and TrackThing. GL Cycling I use to record my miles and times on. Yeah I know it's manual entry but for now it is ok. I am waiting for an update to be able to export out of the iPhone to my Mac. It is meant more for someone just learning some things about bikes. Not recommended for experienced riders as you have to wade through several screens to get to the tracking log.

I have not used TrackThing yet but that is next to be tested.

Trailguru is clever but sometimes incredibly inaccurate. One of my Max Speeds this week was 149 KPH. Sweet! No wish for that to be true but seriously I am just getting back into shape as a a commuter on a very short commute to the Shuttle Bus stop nearby. I am not a long distance rider yet but am working my way up there very slowly. The Altitude/Elevation display in Trailguru is interesting. I knew I was struggling up hills and wanted to see the numbers. There is no percent grade though just feet or meter changes. I would love to know that information before I go out and discover a huge hill on the route. Being a little new to this and not yet in the best of shape I dread hills but am getting better with them.

One nice feature about the trailguru.com website are the topo maps. The maps are detailed so you can see terrain changes. YMMV with trailguru. So far it's been enlightening.

I also tested RunKeeper. Handy but not as accurate as my bike computer (none of the iPhone apps are close to the bike computer for accuracy).

There is a way to alter the number of data points the GPS picks up.

I reloaded iTrail which has an option to alter the GPS interval. I am not entirely sure if this sets GPS to that interval for all app's or just iTrail. When I was first testing iTrail I was having issues with it quiting. Now that I think that issue is resolved I will try it again. Anyway there are lots of apps for the iPhone. Some work well in some ways others in other ways. No one app does it all.

I doubt seriously there will be a HRM or cadence recording to go with these apps as it would probably require too many things running at the same time? Guessing on that bit. There are likely to be some serious programming challenges for all the functions everyone wants to squeeze into the iPhone for cycling. For now I am still in experimenting phase. If I can get this to work that will mean I only have to carry one thing instead of all the gadgets. I can dream.