Suggestion: Turn on +RTS -xt by default
I found it quite surprising and difficult to debug that my heap profile showed no leak while the GC stats showed a clear leak. As a user who is somewhat familiar with this stuff, I was quite surprised that those two data sources didn't agree. I wasn't sure how to determine why they disagreed, since none of the output referenced anything interesting.
I'm not familiar with the reasoning behind disabling -xt by default, but I think it may be easier for users to figure out that they need to *disable* it (since they'll be able to see its results in the heap profile) than to figure out that they need to *enable* it.