Well, it seems that there are a lot of Windows users that really like Picasa, so having it available on Linux might compel them to switch, since they don't have to stop using Picasa if they really really like it. I personally would prefer digiKam or F-Spot as they are native Linux apps, but I think both of them have a few issues when an average user uses them, digiKam needs a clean-up of it's menus even for me it's seems overly complex while it's not necessary, and F-Spot is still not at what I would consider production quality, if you watch Nat Friedman's demo from DesktopLinuxSummit 2006, you'll see F-Spot crash multiple times
I don't have a problem with Google making Picasa available on Linux, and heck even on *BSD since it runs with the help of Wine, I seriously doubt I will ever use it, because, as I've said before, I like using Free Software, and as little proprietary stuff as possible*, and since I'm a big fan of the close integration between apps that you'll find in KDE, digiKam suits my needs better, despite the fact that I find the menus a little too complex when they don't need to be.
When I first heard that Google was going to be using Wine to make Picasa available on Linux, I thought it was lame, but now that it's almost done, I've actually changed my mind a little about this. I still say that a native port would have been better, heck had they licensed Qt4 from Trolltech and not used any OS specific stuff on any platform, they just needed to do three compiles to have it on Windows, Mac and Linux. I know this would have been a shitload of work at rewriting, but WTF right, it's free advertisement for Google in the end. Despite this, I'm actually fairly happy with the outcome, not because of Picasa, but because Google has contributed 225 patches for Wine to the community, which I think will help Wine in the end, here you have a an app that was written for Windows from the beginning and hacked/tweaked and linked against a tweaked/patched Wine so that it will run flawlessly, that can only be good to the community, because making Wine better, might help new users migrate to Linux I think.
*) I've counted the total number of non-Free stuff I use, and this is it:
The NVIDIA driver: Free Software is very important to me, but my vision is more important, and using NVIDIA's driver seems to produce a better picture and more visible fonts.
Sun Java: I'm an Azureus additct, but since GNU Classpath and GCJ are getting very good these days, I think I can get rid of Sun Java in the near future, and MAYBE if Sun holds true to it's statements this time, with Scott McNealy out of the picture, and open sources Java, then the problems is completely solved.
Macromedia Flash Player Plugin: When Gnash gets to a point where it's reliable, this one will be tortured with a hex editor and throw out of my machine.
RealPlayer: Seems to work the best for my amaroK uses, for some reason Xine crashes amaroK from time to time and GStreamer support was dropped in 1.4.0, plus I sometimes run into some weird stuff that needs RealPlayer.
w32codecs: This one I probably won't be able to get rid of anytime soon, so we'll have to wait and see what happens.