Finn is popular in 2010 (I'm guessing) cause it's the name of one of the main "hunky" male characters on the show "Glee." So I'd imagine young new moms (think maybe twilight type fans?) are latching on to it.
That said, I named my daughter a "top 20" name back in '08 and while I know a few other girls named Ella in my circle of acquaintances, she has no peers with that name currently (at age 3) and as she gets older, at this rate, I'd say she might have 2 or 3 at any given time in her life, and not necessarily in a "2 other girls in my class" type of way but in a "2 other girls in my whole life" type of way. Which is acceptable enough for me.
Growing up, MY name was pretty unusual. I only knew 1 other girl my age named Leah and we weren't really friends or anything. I knew an adult woman with the same name. And as an adult myself, I have met 1 other Leah. So that's 3 in my lifetime. But guess what? "Jon & Kate + 8" came out however many years ago, and guess what name suddenly appears on the popular lists? Leah. So I'm starting to see babies and toddlers with the name.
Don't discount the power of TV shows on the masses and their perception of names. A hunky guy that sings, or an adorable half asian baby girl can make somewhat obscure names suddenly very appealing.
And also don't discount the lessening power of "top" names these days. I read an article (posted on here) the other day about how in the '50s every single class had a boy named James (in the top 5 names.) While today, you'd have to search six class rooms to find a Jacob (current top 5). So like I said with my daughter's name...yeah, it's popular right now. But popular is a lot more relative than it has been in the past.