I find the twitter example application from the book really nice, but choosing it is really a commitment that has to be carefully supported. The backend service is required basically throughout the whole book. Please fix it! Install Zabbix/Nagios or whatever, have someone to get up in the middle of the night to fix it, if it fails. Otherwise it is just an amateur approach to the serious commitment and does not make you look good, causing a lot of unsatisfied and angry readers. Alternatively setup "student" accounts for the services that can be used instead of http://yamba.marakana.com/api.
PS: I did not succeed to use the http://identi.ca/api mentioned somewhere by the author with the delivered jtwitter.jar. I think that the API is not compatible or I am just missing somehting.
Make your readers happy again and thank you in advance.