So, "a hotel" or "an hotel"?

(English is my third language, after spanish and italian).

Took a revisit today on "extent" versus "extend" at http://www.merriam-webster.com/dictionary/extent

Yup, that's how it was... to the extent of me knowledge, if understood correctly :O)

I think the mistake I make most often is simple singular/plural verb correspondence mismatch - is/are, was/were etc. Especially in phrases like "this group of people [was/were]" - "this group" is singular, "people" is plural, and it's not always clear to me which of them the verb should correspond to.
Normally I just make the verb correspond to whichever noun is closest, but that doesn't always work

My second most frequent mistake is (I guess) with prepositions - for example the distinction between 'at' and 'on' doesn't exist in my native language. More generally, I get the impression that languages assign prepositions to use cases more or less at random, so the chances that you can reuse the prepositions you know when you learn a second language are slim.

My English teacher once told me that my English was a curious mix of relatively advanced vocabulary and phrasing on the one hand, and plenty of simple beginner's mistakes on the other.

I guess some things never change

my most common stumble is words that are not officaly words but people use them a lot of the time like

Alot
cause

and a list like non-words http://www.mindspring.com/~jimvb/nonword.htm#frontground

Being only an English speaker (despite having studied a couple of other languages in my distant past) I have great respect for those who are fluent in more than one language. Having had to read and correct many business related reports and communications over the years I am sensitive to the proper use of English. I have been quite dismayed by the mistakes even supposedly educated native English speakers make, especially when the report is to be used professionally. I find some of the posts by non native English users to be quite unintentionally humorous, but I always need to realize they are doing much better in English than I would be doing in their language.

To all of you, keep up the good work.

Cheers