As you could see I've completed too the migration from nGallery to CommunityServer, without major incidents and data loss.
I've used a migration utility which is sort of official, of course I found a bug, when migration comments they assumed that Anonymous user has the ID 1000, but this is not anymore true since CommunityServer 1.1 at least (in 1.1 the IDs start at 2000 or 2100).
Also I've noted that this utility when it gots an exception from the CS code, it simply hangs and nothing happens. I had to investigate this since when I was migrating the old gallery, it appeared to stay indefinitely at the second album picture 14th. I thought that it will take a little bit longer, but left it a few hours and nothing happened, and no error message. Well, the code crashed since that was the first picture with a comment (a spam anyway) since it was trying to add as originator of the comment the user with ID 1000, which did not exist (oh yeah, foreign key violation).
Another thing that I did no like, and I think that I will update it manually, the fact that it doesn't keep the original dates, where the picture was added. I think this is a limitation of the fact that this tool uses the existing CS code, which does not offer a posibility to change the date. I will go directly to database sometime in the future to adjust the old pictures, only a little bit over 100 pictures have to be adjusted.
One of the most annoying "feature" is that you cannot import album by album, but all albums go into the same gallery, which is not neccesarly a good thing. Since I was tweaking the code, I've introduced a quick if to ask the user (aka me) if a specific album is imported or not in the selected gallery. This way I was able to migrate 1 album to 1 gallery, and luckily, I had only 7 albums or so. If you have large number of albums this hack will probably cause more headache than solve.
I've used the url rewriting component found via Dennis van der Stelt also, to fix all the old links that pointed directly to albums, so Google & friends would be able to pickup changes more rapidly.
An important feature that is missing in the CS is the bulk upload. I think I'll use CS_FTP to a temporary folder on my desktop, and afterwards upload it to the hosting server, otherwise I will minimize drastically the number of uploaded pictures.
This being told, you are welcome to see my new galleries.