I did see a longer than expected Saving yesterday, and also found I could continue modeling while that was going on. I was testing a larger than typical model at the time. I have a theory about what is going on, Mark can let us know if I’m remotely on the right lines.
When you click Save there are some number of seconds while SketchUp gets mentally prepared to do the save. After that it will be uploading the model, so that it’s saved online. That’s when you see the Saving message. You can continue working during that time. When Saving goes away it will most likely say Save, unless you have done no changes, in which case it will say Saved. Do any changes, and it’s Save again.
So, times when it is apparently stuck in Saving could be when you have a large model and your Internet upload speed isn’t ideal at the moment. A good way to work might be to proactively do a Save, wait for it to say Saving, and then carry on with your next changes. No matter how slow your Internet is, it hopefully will be back on Save before you are ready to save your recent changes.
I tried leaving the model alone for a while, to see if an auto save also showed the Saving message, but that didn’t happen. Mark has mentioned that there will be auto save options added, once those are there you could set it to auto save every five minutes, or whatever you prefer, and at the five minute mark things will appear to lock up for a moment, Save will change to Saving, and you can carry on working again.