Hello,
I'm writing this post for fews reasons.
I'm currently using Nintex Workflow 2007 and think it is very useful (and mandatory if you use Workflows in SharePoint 
).
However, probably because in my company we have specific needs, I've found possible improvements (in fact it's just ideas that I'm sharing, not a request for next release or something like that).
First, when we use few boxes "Set to variable", It could useful to regroup them in one. "Action box" could do this but if in a single box "Set a variable" you could set not only one, but as many variables as you want (like conditions in a "Set a condition", with a "plus" option to add other variables to set, for example, it could be nice for the design (less boxes). Just an idea, not useful for the workflow, but for reading it. (I'm aware that when you put the mouse on the box, with this you couldn't display many variables ... but just the name for example).
Then, for the "request approval/review" and the same for Flexitask, a way of waiting all responses, even if their some people that agree and others don't. Actually if you want that all reviewers say "ok" to go to the "Accepted" way, if one say no, other are "no longer required". An option to let them response even if we know that it will go to the "rejected way" could be useful for some case (we want point of view of all reviewers).
And in the same boxes (actually it's very specific but ... could help some cases) a "special reviewer" that normally don't give opinion (optional), but if he answer to the task, only is answer will be taken in account. Like a "manager" that bypass all others reviewers.
Just to finish, but I'm not sure that it is not available actually, to have "Last Approver Comments" in html (I just see it for all approvers comments in the worfklow, not the latest.
That's all.
I hope this could help you to improve this great product, or give you ideas 
.
Regards,
Adrien T