Yup, reinstalling tends to call up the steam guard too.
Freetrack doesn't seem to like win7 x64 much, it crashed while steam was updating and it messed it all up (it would hang on the update bar and not load the client), so i went to their support section and followed the advice to delete some files.
Apparently that resets Steam to the base version i had initially downloaded, so when i launched it again it updated again from scratch. All fine up till now (except forgetting my login details and fumbling around a bit with that, but that was my fault).
Once i logged in i got the steam guard notification.
It seems that reinstalling or wiping certain configuration files gets rid of your unique ID for your PC and a new one is created, which results in steam thinking it's another PC.
Thankfully i didn't have to try a second time and all the automated emails took less than a couple of minutes to arrive: i didn't know there is a 24 hour limit between subsequent steam guard codes and if i had messed it up and i requested a new one i'd be in panic mode waiting for that email
On the bright side of things, it seems that steam guard doesn't just change the allowed PC ID for your account but adds all the IDs you verify to a pool (according to their on-screen messages), which means that once you verify them you can log-in from any single one without going through it all again.
Not useful for everyone, but i can see it being used for people with multiple PCs (work/laptop and home desktop) or those who would like to use PCs of friends (at lan parties or visits) with their own steam account without risking getting it hijacked.