I am looking into replacing my R40 for an R400 or R500. I am leaning towards the 400 because of it's smaller size and weight. Anything I should know about these two? Pros and cons, opinions, etc.?

The only real drawback to the R400 is that only the 4 cell battery fits flush in the base. That battery is good for a couple of hours. If you want a battery with longer runtime, like the 6 cell, 7 cell or 9 cell options, then it will stick out the back quite a bit. The 6 cell and up batteries are also heavy. The same holds true for R61, T61 and T400 models.

FYI, the 6 cell battery sits flush in an R500, while the 9 cell sticks out. Those are the only options for the 15.4" models. (Batteries are not interchangable between 14" widescreen and 15.4" widescreen models.)

Reading online, I see that the R500 is quite a bit bulkier than the R400. How would the R500 compare to my R40 in terms of size and weight? Looking at the specifications it would be slightly larger in width and depth, but smaller in height and weight. that would be okay, the size of my r40 is perfect and i would appreciate a widescreen display. anything else to take into consideration?

I think the reason to opt for the R500 is if you want the WSXGA+ screen and don't need much mobility.

I wouldn't be traveling too much with it, and I'm used to traveling with this clunker. WSXGA+ sounds nice but screen resolution doesn't bother me too much.

R400 have smaller differences than T400. Google it you will find many website comparing between the two.

As a previous R400 long time user, this machine have served me well. Build quality is solid with thinkpad characteristic weakness : some flex near the ultra bay if you press it hard.

The R500 is pretty close to the R40 in thickness. I think the R500 is slightly thinner, and heavier. You would think that after 5 years it would get a little more thinner.