I guess some of the info I posted last year caused some contraversy so I'd like to add an update. This year Shimano has been even clearer about the intended use of each component group and has added the following to their 2012 Trade Sales & Support Manual under Classification of MTB riding styles:

"WARNING
Don't use a bike equipped with casual MTB/City Bike components on aggressive off-road trail.


ALIVIO, ACERA and ALTUS components are not developed for serious MTB riding, while making a clear distinction with the high-end components such as DEORE and SAINT groups in terms of purpose of use.


For instance, the use of a bike equipped with ALIVIO or ACERA components for aggressive riding may cause damage and possible injury.


Also, TOURNEY components are the MTB-look product group for casual city riding on paved roads. We will appreciate that you understand the product level and intended use of each component group and please give guidance to users on safe riding"


So the bottom line is that anyone trying to sell you a bike with any of these components and suggesting that it's suitable for aggressive MTB riding is either uninformed or just wants your money. And unfortunately Shimano doesn't have to honor warranty claims made on components damaged while being used for anything outside their intended use.


It's your money and when you spend it you should at least get something suitable for what you plan on using it for. In fact you should insist on it.