guess its pot luck, my battery still lasts 3 hours, the fan is barely audible most of the time and i've added RAM off ebay without issues. agreed it comes with shite on it but i just wiped it at the start so i could start fresh.
Had your dell broken down your warranty would have been invalid if you'd put new ram in, unless it was dell ram.
How much was your laptop btw? Mine was one of the 'cheaper' ones at the time (3 1/2 years ago) and it was about £800 I think.