I'm not going to be a pedant and just assume that without specifying a region, the use of 1000 means 1000 AD, and therefore you mean within European Christendom, since the date would have little importance elsewhere.

The answer is not much, because even though the Gregorian Calendar was up and kicking, that system of time measurement was not particularly popular with everyone, with time based around the coronation of the Monarch being more prevalent, (for example 1000 AD would probably be described as the 17th year of the reign of Otto III as King of Germany, or perhaps his 5th as (Holy) Roman Emperor) It's been said that there was some worry that the world would end of the thousandth year after the birth of Christ, but that this was mostly confined to a few "uneasy French Monks" (Cantor, 1993, Europe in 1050 p235) 1033 AD would see this anxiety to a greater extent, being the Millennial of the death of Christ.

Pinging /u/haimoofauxerre , /u/savvysioux.

Mentioning previous replies is not intended to discourage discussion. Further questions, info, and debate are welcome. Especially here, where there is disagreement in the entries in the FAQ section 'Were there any "new millenium" celebrations in the year 1000AD?'.

I think this one is the better of the two replies there:

"Did people in 999 AD celebrate the new millennium? Were there any doomsday predictions similar to Y2K?" at https://www.reddit.com/r/AskHistorians/comments/1powhu/did_people_in_999_ad_celebrate_the_new_millennium/cd52461/ , reply by haimoofauxerre

The FAQ has another link, "Was the millennium from 999-1000 ad marked in any special way?" at https://www.reddit.com/r/AskHistorians/comments/53sxwl/was_the_millennium_from_9991000_ad_marked_in_any/d7y708j/ , reply by savvysioux . BUT: it is written in an absolute way ("People thought"), and I gather from the above that it follows the older historiography. The previous one's measured "some people" feels a lot more plausible, though I'm not an expert. But at the very least, this can give you a few details about what Ralph Glaber wrote.

So I really do hope for more discussion.