Google Operating System is reporting that Google has upped the maximum Gmail attachment size from 20MB to 25MB in the past week. Considering the ever growing size of files, increasing the size of attachments allowed on Gmail is almost necessary.
Personally, I find 25MB still a bit small but I guess it is reasonable. Beware of the flash uploader for these larger files though as it tends to fail on many items over 10MB. It is best to use the old uploader.