I am standing on the diving board, as soon as I see lots and lots of my favorite extensions available for 1.5 I will dive in. Till then the water is a little cold.
I think Joomla should create another extension section devoted just to 1.5. It gets a little old searching for them.
I like may others have been playing with 1.5 for a long time. The last RC(4) was very clean and I have been updating with nightly until today when I loaded 1.5 stable. My approach to my upgraded site was to depend only on what was in the release. Of course I have the latest release of my favorite RocketTheme template VIII for 1.5 native. I have also added a few 1.5 native extensions that are not mission critical for Google ads etc. If it didn't load and test pure 1.5 not legacy it got the boot.
The upgraded site is missing some extensions that I want in my final design but the basic Joomla look isn't bad. It has allowed me to clean things up and begin refining content. I elected not to migrate data but to move individual items. It has encouraged me to cleanup, optimize content, begin adding deep content linking and leave behind a number of my bad habits/hacks.
I am hopeful that as the true native extension I am waiting on arrive they will fit right in. In the mean time I am happily polishing content to hopefully improve my SEO. I do need to hide one of the recent RT extensions that depended on a newer template than I am using to work, it surprised me a little as I expected convention to be that an extension would bring with it everything it needed to work clean but the notes do say it was released only for the current template.
I have found 1.5 to be very "stable" clean. I have been especially pleased at the code it generates. Clean html under the covers. I have turned off the editor and freely cut and paste content from DreamWeaver into the unedited html box.
I am to the point that I am going live with my 1.5 site and will continue in my test bed to add extensions. I'm ready not to have to deal with but 1 code base and 1.5 has shown it is the better place for me to be. Several of my other sites will have to wait on key additions before they make the leap but I hope that will be soon. The biggest one of which is iJoomla magazine which I am waiting for signs of movement from after they got burned by the GPL/commercial issue and a little move volatile early RC than they wanted to develop for. I had aways used a mixed of things I paid for "commercial" and open source stuff on my sites.
I have put the word out the last security update was my last change to pre-1.5 sites. I have a couple of missing menu pages in the first site which just don't go anywhere public until the needed extension arrives so I have either unpublished them or where I needed them for layout they just don't do anything. No coming soon. Soon was today. I am actually to the point I loathe having to deal with 1.0.14 and am moving the other sites content to 1.5 behind the scenes while I wait on extensions. The only remaining work I have to do in obsolete versions of Joomla is to make some archival screen shots, backup (directory & db) for archiving and then rename the directories to replace them with 1.5. After a few weeks of stable usage I then remove the old directories and databases. I am hopeful that the needed native extension are closer than I fear because I'm ready to be ALL 1.5 ALL the time.
You are welcome to check the site out and please let me know what I missed in my 1.5 conversion.