Im one of the people who totally agrees with you. I don't understand why all the rush is necessary. To be honest with you, I sometimes go as far as to think that the people that use such abbreviations are either unsure how to spell a certain word, or are just slow typers / keypadders (on a cellphone)... It doesnt make sense why anyone would want to eliminate two or three letters from a word to get it typed faster at the expense of sounding totally unprofessional, informal, and well... immature...
I personally prefer typing entire words... Occasionally removing the last letter of a sentence ending in ING and replacing the G with an apostrophe -> '
I must however say that sometimes, when Im using SMS to send a message... each msg has a limit of up to a certain number of characters... Sometimes if i go over the limit, and thus going into the second SMS msg... as to save money, I go back and delete a few last letters in words, and do use 2, U, ppl, etc... In that context, I can understand why one would use it... But on the whole, for instance while chatting, you are not charged per character you use, so I can't see why one would use these abbreviations at all.
And you are right... the impression you get from chatting with someone who uses these abbreviations is that they are either young and immature.