Ubuntu 9.04 supports; the ext4 file system which allows up to 64,000 subdirectories, one Exabyte volume, and files up to 16 Terabytes. Ext4 also adds two bits to the time stamp field thus delaying the Year 2038 problem for 500 years, allows faster boot times and has improvements over ext3 file systems in preventing disk fragmentation.
I've been using Ubuntu for several years and am pleased with it. It's not perfect but no operating system is. It does almost everything I want with the exception of running iTunes and occasionally not being able to open some videos on a limited number of websites. Open Office works fine for the word processing, spread sheet or presentation type work I want to do. Gimp is a very powerful photo editing tool, Picasa is good for organizing and minor photo retouching and there's a ton of other free applications available. Support is good because the people who post questions and answers on the Ubuntu bulletin boards tend to be people who know something about writing or modifying code...or at least aren't afraid of playing with a computer and learning something new.
One of the interesting things about Ubuntu compared to some other operating systems are the system requirements needed to run this version of Linux. For example, there are other flavors of Linux that require even less memory, but Ubuntu will run reasonably well on a computer with 256 Mb of RAM. This may not be fair but I think there is an inverse relationship between the amount of memory taken up by an application or operating system and the elegance of the programming, and therefore to some extent it's usefulness and reliability.
Mainly I just like Ubuntu because it's free, fun to play with, and it works fine for what I need an operating system to do.
I'm using Ubuntu 9.04 pre-release version and so far it's working fine. I think it boots up and shuts down quicker than the last version Ubuntu 8.10 (Intrepid Ibex) even though I didn't change to the ext4 file system. Canonical provides a new release for Ubuntu every six months, one in April and one in October. Ubuntu 9.10 (Karmic Koala) will be released October 29, 2009.