Files downloaded through the web browser are stored on the sd card in "download“. All apps that you installed are in data/apps, pre-installed apps that came with the phone are in system/apps. Anything sent to you by Bluetooth can be found in the Bluetooth folder on your sd card.
I'm not sure if it's HTC or Virgin Mobile, but mine appears to have a weird file structure. Pre-installed apps are indeed in the system/apps folder. Both the /data and the /sdcard folder are totally empty. Several apps have failed to work because they say they can't open the /sdcard directory. Still haven't found the Bluetooth directory.
I did some comparing to my Acer Android tablet. On the tablet, the internal memory is called /mnt/sdcard. The aftermarket SD card (if mounted) is called /mnt/external_sdcard. Many of the apps I've installed created their own data folder called /mnt/sdcard/"app-name", so a note taking app, for example, keeps all it's notes in that folder. My HTC One V apparently calls it's internal hard drive something other than the standard /mnt/sdcard??
I coped all the program data files from my tablet (/mnt/sdcard/"app-name") to the root directory of the external SD card, removed it from my tablet and put it in the HTC. Bingo!!

All my apps started working just fine. Please note that I'm running ICS on both the tablet and the phone and had updated the exact same apps on both devices before trying this.
I have concluded that my tablet calls the
internal memory /sdcard. The HTC calls the
external memory /sdcard. The tablet has an 8 Gig internal drive and will run just fine without an external SD card. Well, unless you're storing videos or something

The HTC only has a 4 Gig internal drive and it
requires an external memory card to be mounted, because many apps will look to the
external SD card to store all their data. Given the phone's limited memory, this is probably a good idea, but it took me awhile to figure out how it works.