I had some issues with sluggish loading at first, but once in, I could see this having potential! My thoughts right off the bat:

• Does it have to integrate with Facebook? I couldn't turn off "Facebook connect" in the settings. Is my activity on Tripl at all going to show up on Facebook (e.g. newsfeed, notifications) or be sent to my friends? Are they going to receive anything Tripl-related? I don't necessarily want them to know about my trip or that I am using Tripl. Spam would ruin this for me.
• When adding my trip, it seems to only accept very specific information. For example, it won't accept simply a country name like Tanzania, but it will take Dar es Salaam, Tanzania. Additionally it seems to require exact dates. I can understand why it's like this from a technical perspective, and perhaps it is necessary for connecting people. But for travelers like me who don't have a predetermined itinerary, and who may not stay in any one place for very long, this is difficult. So something that would allow for more flexibility would be great. I want to be able to say I will be in Tanzania for a month, rather than specify every single city I will visit with guesses about dates and a motive for being in each one. Or maybe something like this.

I'll will explore more and give more feedback if I think of anything. I like the idea!