30GB? well, leaving 10GB free at all times, that leaves 20 for the OS.
Sure Win 7 can be squeezed down to 3 or 4 on it's own, but assuming you have 4GB of RAM, there's another 8GB wasted between the swap file and hibernate file, another chunk for snapshots, and then you can start installing apps... just what I grab from Ninite I considder essential, plus a productivity suite, rippers, etc (not to mention the 700MB for the HP drievrs and scanner software) and you can easily chop off another 5GB.
When i installed 7 a few months ago, by boot drive has 22GB on it. I only installed one game (which is stupid NOT to put on an SSD, but apparently that's their intent) so maybe i could have cut that back to 18GB. I manually moved each of the My Docs folders, my OST file, and anything else reasonably portable to D:. Today, my C: drive is well over 40GB. The bulk of that is crap Windows MAKES on it's own, that's not portable. Stuff in Local Apps folders and such, plus bloat from patches and updates to all the core apps, browsers, etc.
I learned the hard way even with Vista, even 32GB was not enough, and on that build the ONLY thing that got put on C: were apps required to load at boot (I used a G: drive for all other apps, including office, games, etc, anything that had to be manually launched). After 6 months I was out of space on C:. I upped it to 80GB and it ran nice at about 50GB full.
30GB is WAY too small for a boot drive today. Even my heavily locked down corporate image drive with XP is using more than 30GB and all my docs are in a home folder on a server... All that's on this machine is office apps, acrobat, CA unicenter, a few java apps, and antivirus...
I'm not even considdering an SSD below 120GB.