First thing first, I got my N900 yesterday... love it!

Now, on with the post... I currently don't have a wireless router, therefore, I can't really hook up my N900 to any WiFi (feel free to suggest a good wireless router). Luckily, as one of the perks for the company I work, I get really cheap and unlimited data plan (although it is GPRS)

While trying to update my N900 from 2.2009.51-1.002 to 3.2010.02-8.002, I had to download 16MB package. During said download, I received several network interruptions with "Download failure"/"Operation failure" messages.

Interestingly, on the first attempt I had 16MB to download, and on my second attempt I only had 6MB download... Is it correct to assume that maemo5 downloads multiple packages or allows for resume of package download? (why did download size went down?)

After the download was finally completed, I received several more "Operation failure" pop-ups, at which point my N900 updated itself. After rebooting, it said that update was completed successfully. (Why did I get those error pop-ups, what exactly went wrong?)

What I am getting at... And I don't know what kind of failsafe maemo5 has in terms of corrupt packages, poor networks, etc... How do I verify the integrity of my device, to ensure that all packages/components/etc are of correct integrity and of correct version?

... Should I just not bother and re-flash my device instead?

You could do that anytime, but no need to do it now.
Without knowing the exact error messages it is difficult to analyse your situation.
But: The underlying process of the update is using some temporary download cache and is able to resume on partly downloaded packages. These packages are checked against md5-sums before installation to verify that everything is okay. MD5-sums are never correct if your download got corrupted. So if there is no md5 mismatch detected the downloaded package was identified as complete.
I dont think there is reason to worry for you.

Please post the log from within Application Manager.

I get Operation Failed all the time with App Manager. It went down after 1.1.1, but initially it kept doing that. No actual errors ever happened. There's a bug report for that.

N900 resumes all downloads that were interrupted, behavior comes with apt.

In theory, it's impossible to corrupt a download, as TCP is verified upon arrival. Also, IIRC BZip has error checking. Also, as stated, MD5 is also there to check stuff around.

Finally, I very much doubt you can successfully complete a corrupted installation.

I did take a look at app logs, at the time, they were empty.

As ndi has stated, in the previous post, it was a bug in pre 1.1.1, which my device was on. I was trying to update from 1.1 to 1.1.1

Well, since I was feeling adventures last night... I downloaded Nokia's Device Software Update, and (to my surprise has managed to) re-install the 3.2010.02-8.002 (PR 1.1.1)

By the way, somebody should update the wiki page. The link to Nokia's Device Software Update application points to 404, and it also incorrectly states that you cannot update to the same version as currently on your device. However, it worked for me. No need for flasher3.5

The Device Software Update also incorrectly states that all data on the device will be deleted with re-install, however, I kept all my personally data, while entire OS was reset.