What's going on here? We're telling drush to give us a list of projects (pml) of the type "module" that are currently enabled. We're leaving out core modules, and --pipe will give us a big list of modules we can feed into another command, without all the extra info.
So, you should get a huge list that looks something like this:
Next, we're going to use drush rl to get the release history for each module. drush rl is great, but if you run it within a Drupal 6 site, it gives you only the Drupal 6 release history (which makes sense, but isn't what we want in this case!).
So, head on over to your Drupal 7 installation (told you we'd need it!). This can be a stock install. If you don't have one, you can do a quick drush dl drupal to install a new one.
Now take your long list of modules, and tack it on to the end of this command:
Wow! You'll get a mix of lines that look like this:
No release history available for itweak_upload 7.x. [warning]
And others that look like this:
------- RELEASES FOR 'CTOOLS' PROJECT ------- Release Date Status 7.x-1.x-dev 2011-May-17 Development 7.x-1.0-alpha4 2011-Mar-26 Supported, Recommended
Yeah! Now you have a much clearer picture of what's ready for Drupal 7, and what's not.
Note that as you look at the list of modules that report "No release history" you'll find quite a few that actually *are* ready, but have either moved into core or been consolidated in some way for Drupal 7. So, you'll still have some investigative work to do, but hopefully you'll have a much more informed view of things as you begin the big journey to Drupal 7. And you saved yourself quite a few clicks visiting all those project pages.
Good luck! And as always, let us know in the comments if there are other, better ways to approach this!