I haven't played LBP in a long time and never got around to ModNation Racers, but I've referenced Forza Motorsport in regards to the problem with sharing in GT. As I often criticized with GT5, it's a crying shame how we had to leap through flaming hoops just to share our tracks with but a handful of people because the whole sharing system in GT5 was awful.
If it had been Forza, the entire community of millions of players would have access to courses, rather than just people on my friend list, and Forza would probably allow me to share multiple courses at one time whereas GT5 allowed one at a time, as I recall. In Forza, you can search for the newest additions, oldest additions, most expensive or least expensive (which shouldn't come into play with shared tracks,) most downloaded, and highest rated. If there's a great track that tens of thousands of players are downloading and it's rated really highly, I can easily find it and get it as well.
With GT5, this just wasn't even remotely possible. The best hope you had was to SPAM the crap out of message boards, trying to promote your Course Maker track. Then, if you found people who were interested, you have to exchange friend requests will all of them. Then, all two or three of those people can download your one available track. That's it; a handful of people, and not hundreds or thousands of people. Then you have to do all this over again for the one track you want to promote next. It was all horrible.
I really want to see this business work a lot better in GT6. We desperately need a system like Forza's. Otherwise, our user-created courses are pretty much useless.