I've noticed this myself over the past week, the 1st gen. iPhone running firmware 2.0 is excruciating slow when launching applications (such as: contacts, photos, camera, etc.). It is also becoming more buggy as it would randomly quit 3rd party applications to homescreen or just restart the iPhone.
Personally, I find that speed issue becomes more bearable if I keep the third party applications to a minimum of 6 or 7. However, I find a lot of problems with synchronization with iTunes (ie. Not sync'ing back with Address Book, no option to set backup settings as it takes so long, etc.)
Just so you can rest assure you are not the only one seeing this slowness happening, I found the following links confirming the same thing: TUAW | MacWorld | 37 Signals
PS - On my 3G iPhone, its a bit faster, wonder if its because of better hardware or the slight difference in the 2.0 firmware build.