A little while ago, a survey was held among alumni of the English department of the University of Leiden to find out about their attitudes to particular usage problems.
The items surveyed can be found in David Crystal’s Encyclopedia of the English Language, under Grammatical Top Ten (1995:194):
- between you and I
- split infinitives (to definitely ask)
- placement of only (I only saw Jane or I saw only Jane)
- none with plural verb (none were left on the table)
- different from rather than to or than
- sentences ending with a preposition (that was the clerk I gave the money to)
- I shall, not I will
- hopefully at the beginning of a sentence
- whom for who (the man whom I saw)
- double negatives.
The results of the survey are reported on by Thomas de France in “What speakers’ gender, age, and native language reveal about their notions of English usage norms”, but we are also interested in finding out what you think.
Bridging the Unbridgeable 
I find the split infinitive troublesome in written text, but not in speech. This is because in speech the “to” is generally pronounced “te” as in Dutch, when part of an infinitive. I notice occasional “splits” in Dutch usage, but the only other use of “te” is for the adverb “too”, whereas in English the “to” has several other uses. So a long split in text can leave the reader asking; what sort of “to” is it?