The OSS version is more or less the full version from what I can tell. That said, we're in the process of switching away from it.
Switching to what?
From the workflow I really like PipelineDeals. Unfortunately it's a bit buggy (especially the API). I just started the trial with them last week and if the stuff gets resolved by their customer service I'm pretty sure that's what we'll end up using. I'm planning a blog post which I'll submit here about the various CRM systems that we've tried out (notably SugarCRM, HighRise, Salesforce and PipelineDeals).
That'd be fantastic -- we're trying to figure out which ones to support when.