Please read http://www.dotnetnuke.com/Community/Forums/tabid/795/forumid/118/threadid/316044/scope/posts/Default.aspx where John from powerdnn confirms that they agree that 5.1 and above are stable & producttion ready and that message was an error based on the troubles dotnetnuke.com was experiencing (which were particular to our setup of 5.1 anyway)

Cathal

I have had no problems with 5.1.1. It is stable (previous versions of 5.x I was not so sure about).

There is a difference between difficulty upgrading and stability after the upgrade (i.e. a running site).
Some people always have difficulties upgrading, this is no different from 4.x

I've done one upgrade from 4.5.5 to a live site and it ran pretty smooth, I only had one minor issue whereby I could not export portal templates which was easily correctable. The upgraded production site has run for a week and it is fast and very reliable.

There will be a 5.1.2 out (not sure when) if people want to wait for that which should correct further issues upgrading. People should note there are so many different upgrade scenarios (third party modules are a big factor, and people implementing fixes that could bite back at a later stage) it's difficult to cater for every combination even after a lot of testing... people stuck in upgrade scenarios should either roll back or post here/search forums/search google for advice on how to fix issues.

We should acknowledge that there have certainly been some legitimate upgrade issues for some people. Each version of DNN however should improve on peoples upgrade scenarios (because hopefully they are logging their issues on support.dotnetnuke.com and the issues get noticed). However I think most people have had a pretty smooth ride (unlike previous 5.x versions). If you are cautious then maybe you should wait for 5.1.2...
Anyway, it is YOUR website so YOU should make the decision as to what you should do . If you want to stick with 4.x there will be a 4.9.5 but this only fixes showstoper issues. To contrast 5.x fixes a load of 4.x issues that haven't been fixed in 4.x (and won't be fixed as they aren't deemed as critical, and it would be a complete waste of time trying to back port every single issue esp. when people can upgrade now or later to 5.x). My advice is do a test upgrade on a local machine with your site, and eval the situation yourself.

For me 5.1.1 is a platform I feel confident about, and 5.1.2 should hopefully cement this for other people who may be still worried, assuming we can get most if not all the issues logged in Gemini fixed that need fixing.

Whatever you do please back up before you upgrade.

Thanks...

 I am anything but a dnn fan, but I will say that, thus far, my site running 5 is working much better than when I had created it in 4.9.4.

I'm still losing Session randomly and often, which sucks, but - for the most part - version 5 has been much better for me.

I'd recommend it if only to avoid having to upgrade later as that, from the posts on this board, seems like a huge pain to have to do.