Lion runs beautifully on my 13" MBP, and I really love it. Yes, it has it's little bugs, which is to be expected with a new release, but overall it's excellent.
The question here really is more about your mom. Is she technically savvy? Is this her first Mac?
If she's not tech savvy (as many of our Moms aren't) and especially if this is her first Mac, you SHOULD upgrade to Lion.
You don't want her to get used to using SL and then change everything on her in a month or two. If she's already using SL on another Mac, then this is irrelevant.
The average user will not have an issue with the handful of bugs that are present in Lion.
The people who aren't liking Lion dislike it for a few reasons:
1. It doesn't work with the software they currently run, usually pro apps. This has nothing to do with Lion and everything to do with them not doing the appropriate research before switching. Pro Apps are rarely compatible with new OS software releases, this should be common sense for computer users in 2011.
2. They don't have trackpads. Everything about Lion is based on multitouch gestures. Apple has invested heavily in the concept of multitouch gestures, and they are the future of this platform, there is no way around that and in my opinion it's an awesome move.
3. It's different from Snow Leopard. Yeah, that's right, they don't like the new OS because it isn't just like the old OS. Why this is a surprise, I can't figure out. You can't please everybody.
4. Some people just like to whine and complain. The thing could spit gold coins out when you hit the space bar and somebody would gripe about it.
Long story short, if your Mom is an average user and isn't embedded in Snow Leopard already, then switching to Lion now is ideal. This way she can learn it straight away and not have to struggle with a change down the road.
If she does use SL already, then just ask her what she wants to do. Tell her it's free now, or $29.99 later. If she's very comfortable in SL or uses Apps that may not be compatible yet, it may be worth the thirty bucks to wait.
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Kind of funny how going Full Screen is revolutionary for Mac while Windows has had it forever don't ya think?


Still I agree
It's a different kind of full-screen in Lion as compared to Windows. The stated concept is you get to maximize the screen real estate, but the real benefit is that the full screen app becomes its own "space" or "desktop". A quick three finger swipe (left or right) on the trackpad and you're moving between multiple multi-tasking apps and desktops. On a 13" laptop this is awesome.