Only a few Easters have had a mean CET of 10 deg. C. or greater:
14.5 1949 15th-18th April
13.6 1926 2nd-5th April
12.1 1984 20th-23rd April
11.8 1987 17th-20th April
11.4 1979 13th-16th April; 1992 2nd-5th April
11.3 1912 5th-8th April
11.1 1992 17th-20th April 1992
10.7 1955 8th-11th April; 1976 16th-19th April
10.6 1924 18th-21st April; 1943 23rd-26th April; 1952 11th-14th April
10.5 2003 18th-21st April
10.4 1935 19th-22nd April
10.3 1972 31st March-3rd April
10.1 1928 6th-9th April
10.0 1909 9th-12th April; 1919 18th-21st April; 1945 30th March-2nd April; 2000 21st-24th April
Thus 21 out of 106 years (about 1 year in 5) were >= 10 deg. C., but only 8 were warmer than 11 deg. C. and 3 greater than 12 deg, C.; 1949 and 1926 were well ahead. Note that all these are entirely in April except 1972 (31st March to 3rd April). The warmest Easter which was entirely in March was 9.8 deg. C. in 1948 (26th-29th March); only 2005 (9.5 25th-28th March) and 1940 (9.4 22nd-25th March) had a mean CET of 9.0 deg. C. or greater, of Easters entirely in March.
Perhaps the most surprising "Warm Easter" was in 1979, which was sandwiched inside a long spell of generally cold or very cold weather lasting many weeks from late December 1978 to mid-May 1979. There was a very cold Easter in 1975 (3.4 deg. C. from 28th to 31st March); indeed this was the joint coldest Easter from 1900 to 2006 along with 1917 (6th-9th April) and 1937 (26th to 29th March).
There have been 19 Easters entirely in March, 10 partly in March and partly in April, and 78 entirely in April in the period 1900-2006. I suppose someone could calculate the average CET of each type.
As there is slightly less than a 20% chance of Easter occurring entirely in March, statistically one can hardly expect a "March Easter" to be particularly warm. As there is a significant increase in day length and sun height from late March to late April, one would expect that most of the warmest Easters would be in mid or late April. The warmest "early April Easter" (i.e. between 1st and 10th April) was in 1926 (2nd-5th), which was the 2nd warmest with 13.6 deg. C. and only 0.9 deg. C. behind 1949 (15th-18th April), though otherwise only 1992 (2nd-5th April 11.4), 1912 (5th-8th April 11.3), and 1928 (6th-9th April 10.1) were 10.0 deg. C. or above.
Even the wamest Easter barely approaches the expected CET value of say early June. Reasons for this could 0be that even with warm sunny weather by day, the temperature can fall sharply by night (which are still 11-12 hours long) especially if the ground is dry (as it can be in spring) and of course there is a particular tendency at this time of year for the weather to change from warm to cold in a day or two; one might have a couple of warm days being counterbalanced by a couple of cold ones, either at the beginning or end of the Easter holiday. Certainly 2008 isn't going to have a CET greater than 10 deg. C and it looks like all 4 days will be cold; it might be the coldest since say 1998 (4.1 deg. C.).
Consolations could be (a) Bright weather (b) Some snow, which may be welcome for those who got hardly any this past 2 winters © Weather does not seem much warmer in parts of the Continent, e.g. France and Spain, at the moment.