Converts the mp3s to aac without a hitch however the tags on some of my files, I'd say about a 100, are a little messed up. Also it failed to automatically set up these new files with my itunes library.
Overall, not too bad, but they should really look to fix these issues.

I have a very large music collection of 4500 tracks and growing. Some of these are lengthy opera and theater peices but most are 3 to 5 minutes long. I attempted converting them from MP3 files to AAC using iTunes and found it impractical as iTunes failed to update my library and left duplicate copies in my folders. I purchased AAChoo, dropped the entire folder of 4500+ songs onto AAChoo and stood back. It has been tackling my MP3s one at a time 24 hours a day for several days without a glitch. It runs in the background while other people are logged in doing other work. It has handled complex file structures involving multiple levels of subfolders without a problem. Everything gets converted and ends up in the correct location. AAChoo is a very convenient program and quite a labor saver for me. Even running 24-hours a day it will take it over 9 days to complete the project but I would have never gotten it done using iTunes.

Actually, the bit rate setting is different from the encoding quality setting. iTunes lets you choose the bit rate but forces a faster, lower-quality encoding. Ovolab AAChoo allows you to use a higher-quality encoding, regardless of the bit rate you choose.
In addition, the only setting that affects the file size is the bit rate. The encoding quality only affects... the quality.

Seems it has to be trashed first and fished out again! Yeah, now it runs fine!

Actually, iTunes does not do what AAChoo does. AAChoo encodes at a much higher quality, where iTunes natively encodes at a lower quality. iTunes also doesn't do the task of deleting your old MP3s after it converts it. Other than the occasional crashing problem (which they're working on), you can essentially drag your entire iTunes folder onto this program and it will convert your MP3s at a higher quality than iTunes, and it will automatically remove your old MP3s and update the iTunes database. If you're a person like me who has thousands of MP3s, and who doesn't want to spend the time manually deleting and updating the iTunes database, this program is perfect.