We've build on top of selenium. Traces are modular in a similar fashion than programming parametrized modules and they can be updated separately - Mixing the benefits of programmable tests with the easiness of record&playback.
It's more of a pain in the ass but I can write my own tests with Selenium in Cucumber or RSPEC or what have you, and I can use all kinds of wrappers for it(Watir, TelluriumDriver, etc). I understand the ease of just doing a "trace" graphical test instead of writing the code, but why would I pay you 90$/month for the privilege? Not only that, I can get much more granular with my RSPEC-Selenium tests. Oh yes, I can also re-use methods that encapsulate sequences of decisions like sign_up_for_website instead of having to resign up every time I make a new trace.
I can go through a sign up flow and then grab the last user with Ruby and do actual checks on it's methods and members, and then go back to browser navigation. This seems like a less free way to do fewer checks with a prettier interface.
We're currently providing a way to reuse the beginning of trace in other traces. Most traces start with logging in to the app, so you can create the login trace, and share it to all other traces. So you end up defining signing up once.
I'm surprised a GUI for selenium test creation hasn't been done sooner. It looks like you guys have done a good job, but the feature I would need to see before using this seriously is a way to get the selenium code output and fine tune it. That way most tests could be created by less technical people but if there are issues an engineer could step in and fix it.