I've used ext3 for 2010.7 installation simply so it is usable/readable with other distro's for maintenance purposes. Usually on anothers pc that I maintain. I will use a very small, won't say whos distro, live cd that is exceptionally fast...and doesn't support ext4 yet. I do this because I'm working offsite and in a hurry and this tiny distro, that runs as root, allows me to boot up and fix things fast and get gone. First time I tried this with new 2010 install it would not recognize any ext4 partitions. I was able to repair with the live cd of pclos, just not as fast to boot as it's a full disto.
Now, my personal home rigs are ext4 and I have no other linux distro's, currently installed here, but Pclos that I use daily.
Before I canned my kde3 version I also had this problem of not reading ext4 as I had both versions on same pc as not all my programs worked quite up to snuff at first, but since 10.1 I quit booting to kde3 at all.