First off, I've bought and installed every version of Mac OS X on day one dating back to 10.3 Panther. For the most part, (excluding 10.3 and 10.6) the Mac I was using ran slightly slower, probably by virtue of it being newer software running on older hardware, but otherwise, I've never had any issue with the 10.x.0 releases dating back that far. By the time I'm even able to experience anything that causes me annoyance, the 10.x.1 update is out. I don't even think 10.6.0 lasted more than two weeks before 10.6.1 was released. The GM build runs surprisingly stably, and as others have said, the download-only nature of Lion's distribution will allow them to fix more last-minute bugs. Really, I think that we have little to worry about regarding the adoption of 10.7.0. Also, as others have said, if you don't want to be an early adopter, you luckily have that option. I, myself, will probably not be buying it as I'm going to probably replace the Mac mini Server in my signature with a 15" MacBook Pro and a NAS. Said MacBook Pro will come with Lion pre-loaded, and if I'm not to be using said Mac mini Server for the long haul, I see no reason to spend the $30 on Lion. I'll be definitely installing and running it at work on day 1, but not at home as it doesn't make sense. If it did make sense, I'd be upgrading on day 1 at home as I always have.
The only thing that'd give me pause about upgrading is that I use MacTheRipper 2.66, Office 2004, original StarCraft, Diablo II, Adobe Photoshop CS(1), Quicken 2007. I should acquire a new version of Photoshop, but I really don't want to have to acquire a new version of Office. I downgraded from 2008 because I hated it so much and while 2011 is much better, it's still nowhere near as zippy as 2004. But in the case of the other programs, not having Rosetta will suck. And before you give me the whole infantile "quit living in the past" argument, find me a good reason why they can't simply include a lightweight binary translator. Strikes me as a needless exclusion.
I would also like some official means of performing a fresh install on a new drive. Recovery partitions are cute and all that, but really, they aren't. And it does nothing for me if I have a blank drive. Beyond that, telling me that I'll need to have Snow Leopard handy to perform my Lion install makes no sense, especially when Snow Leopard will have been off the market at that point. Also, what do I do if I'm not a techie and never upgraded from the Intel release of Tiger or Leopard? Or will Apple kindly sell me a DMG that I can download from the Apple Online Store similar to the QuickTime MPEG 2 Component? If you don't like optical discs, I'm all for there being an alternate means of installation, but to limit it to a download to an installer that must run on the machine being upgraded from within the prior version of the OS, that's ridiculous, I'm sorry. At least let me burn or create my own USB disc with the OS Boot/Install disk, and don't hide it in the installer .app itself. The Mac App Store is nice and all, but using it to distribute an OS seems incredibly stupid.