I love MAME. It is one of the greatest inventions in the whole emulation world. I've been using it since the very early public versions were released, and have seen, followed and used all versions develop over the years.
Originally not that many games were supported. I think the first version I used supported maybe a couple of hundred games, but even then it was amazing in the late 90's to be able to fully emulate real original arcade games.
These days I tend to just use MAMEUI x64 (originally MAME32). It is a great all in one MAME and frontend solution. Some of the other branches of the MAME32 code are interesting, but all seem to have slightly different complete rom sets, and MAMEUIs is the one most torrents are aimed for.
I never bother with the interim u MAME releases and only ever update when a new full version is released. And it is so easy to update the MAME rom set these days. Years ago I remember having the hassle each time, of needing to download the latest MAME version update package (which just contained the differences), and then using ClrMAMEPro to rebuild the whole set and try to make it complete. Needing it to rename roms and sets, merge sets etc....
But now that the roms are Torrentzipped it is so easy. I used Pleasuredome to update and maintain my MAME sets. Just download the latest full torrent, point it to your existing MAME rom set, utorrent then checks the files against the new torrent and automatically downloads just the differences and brings the MAME set fully up to date. Normally updates are 1-3GB at most and can be brought up to date in a few hours. Great solution to something that used to be such a big hassle.
CHDs are still however a bit of a nightmare. As mentioned by someone earlier in the thread the whole CHD file structure was changed recently. This was to try and make the CHD filetype more accurate, so it stored each game image more like its original, and more versitile. Originally before this, the CHD file format was only designed to hold HDD stored games, but with the update the format was reworked so the format can now be used to stored any large game data, originally stored on HD, Laserdisc or anything else.
But it still isn't easy to manage and rebuild a CHD set. ClrMAMEPro doens't really handle CHDs that well. Mainly because they are generally just huge single files, unlike rom based games that have more smaller rom files per game that can be managed, renamed and rearranged within the file structure easily. They need to built the functionality from chdman into a new version of this rom manager.
And I think they still need to do some thinking about how CHDs are stored and managed. Something needs to still be worked on to improve them.
CHDs are also not so important to the enjoyment of MAME. More a final huge download for the completest emulation fans among us. A 100GB torrent is quite a size for anyone to download via torrent.