lets do a bit of math...
so instead of 2^80 operations it can now be done in 2^69 operations (for full sha-1)
efectively your dividing the cracking time by 2^11 (2048 non math people)...
i'm still not worried
now taking my bogomips of 4128 (bad measurement... i know, but we'll make up for it by assuming each hash operation equates to ONE cpu operation, which is SOOOOO FAR from realistic)
maccorin@debian:~$ echo "2^80"|bc
maccorin@debian:~$ echo "2^69"|bc
that's how many seconds it would take (under these very unrealistic conditions to crack
maccorin@debian:~$ echo "2^69 / (4128 * 1000000)"|bc
or this many days
or... 4534 YEARS (on an athlong XP2800, at one hash operation PER cpu-operation (*wrong!... it would take a lot more then this, but since we are talking about a constant it can be made up for by faster hardware... so we just pertend we live in a perfect world*)
maccorin@debian:~$ echo "(2^69 / (4128 * 1000000)) / (60*60*24)"|bc
now, while the 9286527 years it would take by brute force is much more comforting... i'd say it's still ok to use sha-1 to check your iso from debian...