What are you referring to? I don't see how the word pocket has any "negative" connotations. It's a little confusing in how it relates to note-taking, but that isn't really negative to me.
* to take possession of as one's own, often dishonestly: to pocket public funds.
* to submit to or endure without protest or open resentment: to pocket an insult.
* to conceal or suppress: to pocket one's pride."
I don't think the negative connotations are exclusively British. I've heard the phrase said plenty of times "John pocketed something", when it meant he kind of stole it. It's also used with regards to politicians sometimes.
The concept is that Pocket (the app) is a could-based version of an actual pocket. Just like you would keep everything in your physical pocket, you can keep thoughts and ideas in your digital Pocket. I veered away from a name involving "note" because I didn't want to limit the app to only notes - eventually users will be able to save photos, videos, bookmarks, etc. I've got some grand ideas in mind =]
http://dictionary.reference.com/browse/pocket