Open Mini’s Hidden Power User Menu By telecominfo.in

There is another undocumented "Power Users" settings menu hidden in Opera Mini. To access it enter the URL config: in Opera Mini's address bar and select "OK" or "Go To". A screen similar to the one in the bottom image should appear.

Power User Settings include

Large placeholders for images.(Default:Yes) If you have images turned off or Opera Mini doesn't have enough memory to load all the images on large pages it will show colored boxes which by default have the same dimensions as the original images. 

Choosing No is supposed to make Opera Mini use smaller boxes which I think I'd prefer. Unfortunately this option doesn't seem to work, I still get the large boxes with it set No. Aside: I'd really wish Opera Mini would follow web standards and display the image's Alt Text when can't display an image.

Fit text to screen (Default:Yes)  In desktop mode, Opera Mini reflows text columns so they fit the screen's width for easy reading. This is generally a good thing but it can make parts of pages look ugly and cause overlapping text, especially in tabbed menus.  Changing this setting to "No" will cause the page to be rendered just like it would be in a desktop browser. While this makes the page prettier, it also means you have to scroll back and forth  horizontally on every line to read text. I tried it and quickly set it back to the default!

Very Useful
Use bitmap fonts for complex scripts (Default=No) Opera mini normally uses your phone's built in fonts which generally have characters for only a handful of languages. If you try to view a Chinese webpage with a phone that doesn't have Chinese fonts all you will see is a bunch of squares in the place of characters. Setting this option causes Opera to render the text of any language your phone doesn't support as an image of the the text. This will make the page load more slowly but at least you will be able to read it.  Apparently quite a few languages supported by this feature. I haven't been able to find a list but users have reported that they were able to view Hebrew, Arabic, Japanese, Chinese, Korean and  Bengali pages using this feature.

Loading Timeout (default:30) This is my favorite Power User setting.It specifies how seconds the Opera Mini server should wait for a 3rd party web server to respond before giving up and displaying a timeout message. There are some slow sites on the web aznd 30 seconds is just too short.  Before this error was added I'd often get a timeout on HowardForums.com or if I asked Bloglines to show all the posts in my subscribed feeds for the last 24 hours. I set the timout to the maximum allowed, 3600 seconds, and now I never see timeouts.  If a site is really down or I get tired of waiting, I just press the right softkey labeled STOP to make Opera mini give up. Pressing STOP works fine on my phones although it can cause lockups on Palm OS devices.  If you have one of those you might be better off setting the timeout to 60 or 120.

Show feedindex (default:Yes) The default causes Opera Mini to show an RSS feed icon at the top on any page that has a feed.  Clicking the icon adds the feed to Opera Mini's built in feed reader.I don't use the Opera Mini reader because it doesn't synchronize with anything and seems to lose my subscribed feeds with every server upgrade.  If you are serious about feeds you will want to use Bloglines or Google Reader as your feed reader in Opera Mini.  I do like to see the feed icon though as it tells me when a site has a feed that I can add to Bloglines using a bookmarklet.
Keep styling in RSS feeds (default:No) As I mentioned I don't use Opera Mini's built in feed reader but I'd think changing this to Yes would improve the appearance and formatting of feeds in Opera Mini. It seems strange that it defaults to No.

Fold linklists (default:Yes) When  Opera Mini is in mobile view it will replace long lists of links with a plus sign graphic. Clicking the plus sign will expand the list.  The intention is to make large repetitive menus less intrusive. I set this to No  as it tends to collapse things I want to see like news headlines or  the list of unread feeds in Bloglines.

Phonenumber detection (default: Yes) Opera Mini tries to detect plain text phone numbers in web pages and turn them in click to call links. When this feature first came out is was buggy and tended to treat "1 2 3 4" page menus on web forums etc. as phone numbers so that clicking them tried to dial 1234 instead of loading the next page.That bug has been fixed and I don't see any reason to disable the very useful phone number detection feature.

Minimum phone number length (Default:9) Numbers less than this length will never be detected as phone numbers. US phone numbers are 10 digits so you could set it to that, although leaving at nine seems to work fine.
While most of the Power User settings are of limited use I'm really happy about the ability to increase the Loading Timeout and to turn off linklist folding.  Although I don't use it (English is my only language) the ability to use server side bitmaps to display character sets that the phone doesn't support is another great feature.  I'm glad the Power User Settings are there although I think Opera should make them easier to find.