3 letter prefixes are outdated and IMO pretty useless. MSDN advises to use the Java naming convention - first letter lowercase, first letter of subsequent words capitalised.
I'm with penagate. There are so many classes in use these days that you end up with 90% of your variables prefixed with "obj", which really gets my goat. If you try to use more meaningful prefixes you end up with clashes which then create confusion rather than alleviate it. Proper variable naming and commenting, plus the features of the modern IDE, pretty much negate the need for Hungarian notation.
The only reason it calls my attention is to be able to quickly find my controls variables using InteliSense. All Forms are organized under frm.. and all textboxes under txt so and so forth.