To answer your question in a slightly different context ...
There are sometimes OS releases that are really solid, relatively. For instance, Windows NT was a very good Windows. But Windows ME was awful. Mac OS X Tiger has to be one of the most solid, put together, coherent OS X releases ever. And it just got better through the updates. (Writing on a Tiger machine now.) While Leopard broke some things (namely, X11), Snow Leopard was pretty solid.
Lion in my opinion is a mess. It seems to be a poorly implemented marriage of iOS and OS X. Spaces have been replaced with less configurable Desktops. The save/save as/export model is very confusing, and there are inconsistencies with whatever it means to resume the state, which has had some hard-to-predict, unintuitive behavior (applications that re-open even after they were closed and applications that open with some saved state even if everything is closed previously). Natural scrolling is not natural for a trackpad model (though is for a touch screen model, and this is easy to configure, although the option was missing on one of my computer's system preferences at first!).
I was foolhardy in upgrading my working machines (MP, MBP) to Lion and regret it. I wish I were still on Snow Leopard. But, I do have hopes for Mountain Lion.
If you have time and are curious enough to want to play with Lion, then it's not like there are show-stopping security concerns that should stop you. But the transition from SL to Lion was a big one in terms of some kind of computing paradigm in which there is a hybrid between mobile and desktop features.
The big thing about ML that I'm wary of is whether or not Apple is going to try to push this RIDICULOUS document model in which applications own documents that have to be exported (is it a copy that needs to be copied back? is it a move?) to other applications in order to use them. There are some suggestions with new Mac App Store guidelines that suggest this. From someone coming from the UNIX applications perspective of one application that does a very specific job very well (cp, mv, ls, etc.), this is going to invariably push developers to integrate every task into one application. Sounds great, until we come across applications that are really good at one thing but really bad at other things, facilitating the need for document sharing across applications. (One example of this is Papers -- great at PDF management and discovery, not nearly as good at BibTeX as BibDesk.)
So, if you have good cause and some spare "time" (I mean that in terms of not affecting your work), then Lion isn't the worst thing you can do, and it will get you ready for ML. But it's enough of a change from SL to Lion and beyond to really consider what one needs.
