Warning about using mgmaps offline!!!

Wow, that is a big map. How does it run on the phone? You said 750mb for just level 17. Are you only using level 17? If you try it and it takes forever to load up get that memory card out of your phone quickly or you will be returning it for a new phone.

Your thanks is appreciated twofold. 

I just created a map and it's currently 944 bytes. Is that less than 1mb?

Well, I accidentally bricked my Impression 6 days into ownership. I was loading maps onto the memory card with the phone. It was taking forever, and I needed to go, so I quit with 1 or two zoom levels to go. I didn't even need to turn on MgMaps before my phone slowed down and froze. Had to take the battery out, and it was bricked after. Took it to Radio Shack and got my new one. Put the memory card in there and it started to do the same thing. This time i took out the card(well I did that last phone too) and checked the internals to find my phone memory was 53% fragmented. A quick reboot and good as new. I erased the maps from the memory card and stuck it back in the phone, and managed to brick that phone too.
 Here's the good part. I turned it on and left it on the startup screen,thinking I'd go to another Radio Shack, and after about 5 minutes it restarted.
So if you manage to kill your phone with this, try just letting it start. Might take awhile, but it might work.

For clarification, putting too many maps on your memory card will in no way brick your phone. It just significantly slows it down to a crawl to the extent that many people think their phone is bricked. It has happened to me a couple of times. Basicaly, once you save the maps on the memory card and insert it into the phone, it starts indexing the files and with hundreds of thousands of small files in large, zoomed maps, it can easily take the phone hours to index them and properly start. Unfortunately, even if you are patient enough to allow the phone to properly index all the files, it will start doing it again whenever you turn off and on your phone, so it will be big pain.
 
I have tested with several collection of maps and other files and can confirm that the problem directly relates to the number of files. These map tiles are very small files, so their number adds up quickly. With maps totalling ~50 MB, it takes the phone 2-3 seconds to index them. For 100-150 MB, it takes the phone 15-20 seconds to index and with my current map (~300 MB), it takes my phone about 45 seconds to index the files whenever I restart the phone. During this time, the memory card icon on top of my Mythic screen is black and you cannot access the memory card or files on it. Once the indexing is done, the memory card icon becomes white and you're good to go.

Anyways, I managed to "brick" my phone by loading over 1GB maps. The solution to this problem was quite straight-forward (and extremely boring): Just wait for your phone to boot (can take hours), then carefully navigate to your settings menu and restore the phone. It will be back to normal and fully functional.

For me, with 1+ GB of maps, it took the phone 3 hours to boot. Then, after hitting each buttom, it took the phone another 10-15 minutes to respond (such a pain, especialy since I hadn't had set up the password and it asked me to set it the first time I was restoring the phone which took like 2 hours with the phone slowed down like this). Anyway, the moment I made it to restore and entered my password, it flashed and restarted and it was as good as the first day.

Hope it helps.
   

You may be right. By being way too slow, the phone is de facto bricked.
Just to re-emphasize, this issue usually begins to occue when you make any modifications to previously indexed files. This can be as simple as deleting some of the files. To avoid the problem, you should never delete the files from the memory card directly. If you have to, either back up all the files, format the card by the phone, make modifications to the back-ed up files and re-copy them to the memory card (sounds tedious, but with the phone connected as mass-storage to a high-speed USB, it won't take more than a few minutes) or make modifications/delete the files using TkFileExplorer (it takes almost as long as copying the files, which I assume gives the phone enough time to re-index the files and avoid the problem)
 
Anyways, I'm sure this thing has been previously addressed around here, but the GMapMaker has an option for increasing the number of tiles per file which effectively reduces the number of files (it put more tiles in each file, so you end up with a smaller number of files which are of bigger size). By putting 32 tiles per file, I have managed to avoid the problem so far and the phone is working nice and fast. I wouldn't take any chances though and still use the methods I described above for making any changes (other than simple addition of more files) to my memory card.