I have Froyo on my HTC Desire for a month now. Its actually my third Froyo phone, following after the Nexus One and then the Droid Incredible. And now I am waiting for my i9000 Galaxy S to get Froyo.
Once Froyo came to my HTCs, the speed advantage of the Galaxy S got lost, although the Galaxy S has this visual and touch smoothness that the HTC phones could not match, which I suspect has something to do with the hardware. I do suspect that once the Galaxy S gets Froyo, you're going to see Quadrant scores in the region of the OMAP3640 used in the Droid 2 or the 8255 Snapdragon used on the Desire HD or MyTouch 4G. That's like way beyond the 8250 Snapdragon Quadrant scores used by the Desire, Nexus One and Droid Incredible.
Furthermore, the Froyo only GMail, Google Search widget and the new YouTube app is really neat. You can watch YouTube videos while viewing comments.
One thing that is holding up Samsung's Froyo update on the Galaxy S, is that it appears they are overhauling and feature adding Touchwiz along the update. HTC gets their Froyo update fast because they are only updating the OS, but not Sense, If you want the new Sense, buy those new HTCs like the Desire Z. To be fair, Sony Ericsson's long delayed Android 2.1 update for the Xperia X10 actually comes with a revised Rachel interface, plus new features added to the phone, like 720p video recording.
So yeah, its wise to see until both phones finally get their updates. Keep in mind that HTC's update isn't going to do a lot of changes with Sense, though it adds Google's News and Weather widget, which is excellent. Some changes on the SMS too, but pretty much, the phone looks the same except what's humming underneath makes it faster. You can now save some specific apps to the SD card as well like Google Earth and Google Sky Maps, to save space since the Desire is rather tight.
The Froyo update to the Galaxy S appears more than just a Froyo update but a Touchwiz facelift as well. We may get additional apps and features throw in too. I like especially to see how it deals with the file system lag problem.
What annoys me with Samsung is that its update has to be driven through the Samsung Kies PC sync program, unlike HTC which is on the air. Note it only affects international phones and users, not US Samsungs which does not use Kies. The update for the US or NAM phones is likely to be over the air.