My gripes on iMac's are as follows;
Slow, ugly, tedious, sod to upgrade, can be unreliable, cheaply built and were overpriced when new. To be honesest I think Apple spend too much on design then actually on decent hardware which seems a shame as the older Mac's were actually half decent, not to mention they were a respetable rival to Micro$oft.
Not to mention the cost of official simple software you'd expect it to come with.