I installed the latest version of Ubuntu on my Lenovo Thinkpad T61 recently. It's codename is "Jaunty Jackalope" but it's normally known as just "Jaunty".
I had changed from using Windows XP as my primary operating system to the previous Ubuntu version, Intrepid Ibex, last November.
For me, the main differences between Windows and Ubuntu were:
+ Boots much faster
+ The command line environment is far superior
+ Installing software using apt-get and Synaptic is wonderful
+ Updates and patches are offered and applied without requiring a reboot
+ Wireless works first time at home (WinXP requires multiple retries - no doubt a driver bug but one I still haven't fixed)
+ An extra clipboard - the middle mouse button pastes a copy of what is selected, without first requiring a Control-C operation to copy it to the "copy" clipboard.
+ CompizFusion - graphical whizziness builtin
+ Multiple desktop support built-in
- USB under VirtualBox doesn't work for iTunes/iPhone, although I have now got it working for my Garmin Forerunner 305 GPS watch
- Multi-monitor management is not quite as good
- Sound works pefectly under WinXP, sometimes distorts in Ubuntu
- Lotus Notes works slightly better under Windows, particularly around window focus
I've kept my Windows partition as is, other than using Ubuntu's Partion Editor to shrink the NTFS partition to free up space for the Ubuntu partitions.
So what's the difference between Jaunty and Intrepid? There is a good page that describes what's new but I've only used 3 of these features: a new notifications mechanism, a new file system technology and an even faster startup.
I'm really liking notifications. When an application detects an event, eg. an email or instant message or Tweet arrives, a simple pop box appears in the corner of the screen. 90%+ of the time I just read it in place before it fades. Unless I need to respond I don't need to switch to the relevant application to read it.
There is more that can be done of course - placement, colour, font, duration are not currently configurable but even without that it's still great.
My aging Windows XP installation takes the best part of 5 minutes before it's started and even then it's still doing things in the background meaning that it feels sluggish.
I did some measurements this evening and my Intrepid installation gets to the logon screen in about 45 seconds, and having logged in I can run a command in a terminal window within about 80 seconds.
My Jaunty installation gets to the logon screen in about 30 seconds, and having logged in I can run a command in a terminal window within about 47 seconds.
Impressively, Jaunty boots in just 59% of the time which makes it about 70% faster.
ext4 file system
This file system can't be ready by my old Intrepid installation, but that's not a problem. The wikipedia page lists the improvements over ext3, including support for exabyte sizes, more sub-directories, checksums in the journal to improve reliability, faster file system integrity checking and nano-second timestamps.
A benchmark comparison concludes that ext4 is faster in most benchmarks but not so much that your average user will notice. They note "What perhaps is more important is that with the addition of the new features, the performance hasn't regressed. Also, when testing the EXT4 file-system, we hadn't run into any problems with stability, file corruption, or any other issues."
A comparison of Jaunty boot times using ext3 versus ext4 on the same hardware showed that ext4 was 11% faster. I'm sure that I won't be seeing that size performance gain in my every day operations but ext4 may well have contributed a few seconds to my improved boot time.
So overall I'm loving Jaunty. Why not burn a CD and try it out? The CD will boot to a working Ubuntu system to let you try it out on your hardware without using your hard disk. Then you can run the installer from there.