I've used both Picasa Web Albums and SmugMug for photo services. I've favored SmugMug for several reasons, including that they're much more serious about color profiles, password protection, backup services, unlimited uploads, and they're less expensive . On the other hand Picasa has much better iPhoto integration. (I use PictureSync with SmugMug.) Most of all, however, Picasa hasn't offered print services.
Tonight SmugMug was very buggy. Not just one repeated bug, but several nasty time consuming bugs. I became seriously annoyed, and went back to Picasa. They offer print services, now, and one of my very first photo vendors, Shutterfly, is a featured provider. (I probably still have old albums on Shutterfly.)
So now Picasa offers reasonable print services, even if they may not be the equal of SmugMug's. On the other hand, Picasa has never been as buggy as SmugMug was tonight...
I'm still moving back and forth, but I'm going to use Picasa for a while. Sure SmugMug wins on big by the feature count, but time-eating bugs are intolerable. Also, they're incredibly late with good iPhoto integration.
 In fact an old blog posting of mine still generates sufficient SmugMug referalls that the service is free for me. If I really do switch I'll have to turn that link off, but maybe SmugMug will fix its bugs.