No I don't think it is very popular, and I've got an Eloise so am probably more aware of the name.
When we named her, we didn't want her to have a very trendy name (therefore also a name that dates) and so we avoided anything in the top 75, and anything which had had a massive rise in popularity. When we looked, the highest placing Eloise had had from 1998 to 2002 was 75th. It mostly sat around the 85 - 100 mark. In fact, the year I had DD, it reached the height of its popularity, at around 75. When I had DD2, and was looking up names again, it had fallen in popularity and was then sitting just outside the top 100. That's where it seems to have sat ever since, around the 100 mark.
On a personal level (although I appreciate that this is annecdotal, so is not exactly statistically valid 
), DD1 was in an infant school of about 275 children, she was the only one in her school. When we moved location, to a primary school of about 225 children, she was still the only one in her school. She goes to a gym club of about 700/800 children and I think I have seen 5/6 children with the name Eloise up on the birthday board at the club. Personally, I know her and two others - both at gymnastics!
In the past, I have taught 3/4 girls called Eloise. They would all be in their early 20s - early 30s now (I'm not that old, I teach secondary, honest ). All were lovely girls.