When using Leopard, I find that certain things make more sense compared to Tiger. Stacks is a welcomed feature. Although it is easily emulated on Tiger, Stacks keeps the desktop clean. The translucent menu bar has drawn many criticism, but the translucent effect can be turned off now with the latest update. Many don't like the 3D dock either, but I prefer the dock to be on the side so it's a non-issue. I still think Windows' Start menu is quicker to start apps, rather than starting Finder (kinda like using Windows Explorer to find and start your Apps). In general, the aesthetics are great and nicer compared to Tiger. Small things like rounded menu edges and higher resolution/better contrasted icons are pleasing to the eyes.
A new feature in Finder that I find very handy is that now Finder can list all networked computers on the sidebar. Definitely provides easier access compared to Tiger's Finder. This also works great with my Windows Home Server unit as all the shared folders are automatically listed. Tiger's Finder feels like a big hassle now. Network drives connectivity are maintained, even after putting my Mac to sleep. However, Leopard still doesn't mount networked drives automatically unless you specifically assign them as a start-up item. I missed Windows' ability to just map a networked drive into a drive letter.
Frontrow now uses Apple TV's interface. Although it looks better, it only shows thumbnails of videos. Frontrow in Tiger will show a preview of the videos. The same alias trick can still be used to allow Frontrow to read files from any other locations in addition to the local media folders. Works great streaming videos from my Windows Home Server. Also since my HP WHS unit has iTunes server capability, music streaming via Frontrow has never been easier.
All this network capabilities are great, but it makes me wonder about security. Well, guess what, the firewall is NOT enabled by default in Leopard. Although there is probably a very low chance of attacks on Macs, not enabling firewall by default is not nice, considering XP SP2 has its firewall enabled by default. Also, Leopard's firewall has a quite confusing interface. There's only 3 options, allowing all incoming connection, blocking everything except essential services, or application firewall. Do a search on Google and there is a lot of controversies and discussions about Leopard's different approach of firewall. Well, choosing the second option made all my networked shares disappear in Finder. Picking the 3rd one made them appear again. We'll see how effective/intrusive this is on a daily basis.
I used a trial for .Mac to transfer my email, address book and calendar from my Macbook, and it works flawlessly. Still not sure if it is worth the subscription fee though.
Overall experience of Leopard seems very smooth. Performance seems to be very snappy, even on my old Core Duo Mac mini with only Intel's GMA950. In fact, IMO MacOS seems to be the only OS where the general GUI experience doesn't fell to be slowed down by the stupid integrated graphic. I have a WinXP PC with the same GMA950 integrated graphics, and I felt performance issues with the regular GUI response compared to a PC with a dedicated graphic card. It doesn't help that most PCs with integrated graphic have low end processors too. Maybe it's the dual core.
I have not tried Time Machine. Have to buy an external drive first. :)
Leopard is a nice aesthetic upgrade from Tiger. Although it draws many criticism, there are just many small pleasant things that contribute to the better overall experience. Tiger is still a fine and solid OS, but Leopard will give you a smoother Mac experience, even on the same hardware.