How long will it take before your software can fully take advantage of the new features of Lion? Granted, it's only been a few months since the first developer previews became available, and not all software vendors consider the Mac platform to be a top priority, but some tools are already taking advantage of the overhauled OS.
For example, Bombich Software's Carbon Copy Cloner (which I find invaluable for replicating the contents of Mac disks) updated last week, shortly after the release of Lion. On the other hand, Microsoft's Office for Mac won't fully support the new OS features for months, said Pat Fox of the Mac Office team in a blog post yesterday. Although comparing the complexity encapsulated in Office to the relatively straightforward processes of CCC is like comparing Trumbull's Declaration of Independence with a child's stick figures, these extreme cases provide a good illustration of the problem.
The good news is that I haven't heard of any show-stopping problems that applications have with Apple's new OS, with the exception of Adobe's laundry list of Lion issues. Even when I look at that, much of what I see appears to be fairly minor problems that will work themselves out in the foreseeable future.
As for those who complain that they can't run applications on Lion that rely on the Rosetta translator: get a grip. Apple sold its last PowerPC Macs five years ago, and made Rosetta an optional download in the last release of Mac OS X. Just as 68k applications gave way to ones written for PowerPC, it's time for PowerPC apps to show up in the rear-view mirror.
If you're wondering about application compatibility, you have two choices: go vendor-by-vendor and compile your own list, or, you could check out the RoaringApps wiki. The wiki, based in Australia, lists in the neighborhood of 2400 applications (if my cocktail napkin calculus is correct), and classifies them by their compatibility and even indicates their availability through the Mac App Store.