I had to write about Lion at some point, right? There are thousands of Lion posts, and I can't imagine I have much to add about its pros and cons, so instead I'm going to write about a few things I like and I'm surprised about liking. I put a developer preview of Lion on my Air a few weeks ago and had a terrible experience with it; it crashed every time I opened the lid on my Air, which made my computer useless. I had to nuke and repave with Snow Leopard---which turned out to be actually useful because I got to use the cool little USB restore thingabopper. So I was wary of Lion, but you know I can't resist the siren call of installing possibly unstable software on my devices, so I put it on my Air first. After a day or two I put it on my iMac, which I wasn't going to do, but there are enough differences between Lion and Snow Leopard that I found it annoying to switch back and forth.
It has been very stable on both Macs. No problems. I just don't use the launchpad because I lazily use Spotlight for most of my app launching, same as I always have. Mission Control is one of the things I didn't think I would like but do. I was a big Spaces user, so it makes sense. I just like being able to flick my fingers and see the inevitable trainwreck of windows I have trailing all over the place.
The autosave feature I thought would annoy me, but I adapted to it instantly and like it. It's a huge paradigm shift, and I had to train myself to immediately find a "save as" equivalent, because I don't trust versioning yet. I will at some point. But I'm an old dog in this case.
Most surprising to me is that I like the new Mail.app and iCal and am using them to the exclusion of their Web counterparts. People are bitter about the torn-paper look of iCal, but I think it looks kind of cool, and the interface has been made usable. You can put in natural language appointments, keyboard shortcuts work in obvious ways, and it plays seamlessly with Gcal, which is what I use. iCal has become more useful than Gcal in a Web browser, and I have NOT been an iCal fan before.
Mail.app...I never used it much because I have a byzantine rules-based Gmail system, I don't like to spend much time messing around with e-mail, and the previous Mail.app was clunkier than the Web interface. The new one has features that make it workable, and it's pretty, and I like having local copies on my Mac. If Google dies it's nice to have my e-mail. Spotlight searches bring up Mail.app mails in a nice readable panes, which is also cool. The main change that makes Mail.app appealing to me is the ability to create smart mailboxes, glue them to the menu bar, access them with keyboard shortcuts, and most importantly send messages to them with keyboard shortcuts. Concretely: I can press apple-cntrl-2 to archive a message because of the way I have my menubar set up with favorite mailboxes. To do that in the old app necessitated plugins. It's not as easy as pressing "y" in Gmail, but it's not a huge effort. So far it's a good tradeoff for me. Data detectors, prettily threaded messages, very workable search and rules, and the Spotlight search previews trump the Web interface.
But that's just me, and it probably only applies to Gmail.
Otherwise, I do like the full-screen option, mainly on my Air. I don't really need it on my iMac, and I don't use it as often as I thought I would on the Air. There is stuff on my menu bar that I like to see. Like the clock. Good to have, but it's not the killer feature for me that I thought it would be.
The Reading List feature of Safari is a big pail of "meh" for me. I like Instapaper and can't see Reading List replacing it. Instapaper is integrated everywhere, already, and can be accessed offline on all my devices. Maybe when iCloud really gets off the ground I'll reassess.
I do like the little iOS-ish gems that pop up, like holding down a key and having the little accent options appear. I'm so used to autocorrect I'm used to the way it works on my desktop, so I like it.
So those are my thoughts on Lion so far. I don't think it's a must-have upgrade, but I also don't see any reason not to do it unless your Mac is a bit long in the tooth. It's worth $30 IMHO.